The probability of a disease or an event/outcome occurring (e.g. an adverse reaction to the drug being tested) in a group of people without the disease or event/outcome during a specified time period. Risk and rate are two different measures of incidence, but the distinction between them is relatively recent and many old studies have used the two words interchangeably. Studies that compare two or more groups of patients may report results in terms of the relative risk.

A term used to describe processes tending to lead to a blood pH less than 7.36. When the pH is less than 7.36, this is referred to as acidaemia. Clinicians sometimes use the terms acidaemia and acidosis interchangeably.

See gastroenteritis.

Blood markers of an inflammatory response

Measurements of the human body or its parts to enable comparisons between individuals of different ages, sexes and races to be made, to determine the difference between normal and abnormal development.

A drug that provides symptomatic relief from diarrhoea. These include adsorbent agents (e.g. kaolin, smectite and activated charcoal), bismuth salicylate, antisecretory agents (e.g. racecadotril) and antimotility agents (e.g. loperamide).

A drug that relieves nausea and prevents vomiting.

A drug that slows the transit of gastrointestinal contents.

A drug that reduces or supresses intestinal fluid secretion.

Inflammation of the appendix.

Formal assessment of the quality of research evidence and its relevance to the clinical question or guideline under consideration, according to predetermined criteria.

See receiver operating characteristic curve (ROC curve).

Relationship between two characteristics that helps to predict change in one when there is a change in the other. The association can be positive (both characteristics change in the same direction) or negative (the characteristics change in the opposite direction).

The strongest research evidence available to support a particular guideline recommendation.

Influences on a study that can lead to invalid conclusions about the study results. Also known as systematic error or deviation from truth. It occurs as a result of defects in the study design or the way the study is carried out or owing to confounding variables. Bias can occur at various stages in the research process, e.g. in the collection, analysis, interpretation, publication or review of research data.

The process of keeping the investigators or subjects of a study ignorant of the group to which a subject has been assigned. For example, a clinical trial in which the participating patients or their doctors are unaware of whether they (the patients) are taking the experimental drug or a placebo (dummy treatment). The purpose of blinding or masking is to protect against bias. See also double-blind study, single-blind study, triple-blind study.

A volume of fluid given quickly.

A test performed on physical examination in which the skin is pressed by the clinician’s finger until blanched and the time taken for the skin to return to its previous colour is measured. Capillary refill time (CRT) can be measured peripherally (in the extremities) or centrally (on the chest wall). A prolonged CRT may be a sign of shock.

A type of observational study that compares a group of individuals with a particular disease or outcome (known as cases) with a group of individuals without the disease or outcome (known as controls). All subjects are then assessed with respect to things that happened to them in the past to explore the association between the disease/outcome and prior exposure to specific risk factors.

A type of observational study with detailed reports on one patient (or case), usually covering the course of that person’s disease and their response to treatment.

A type of observational study with descriptions of several cases of a given disease, usually covering the course of the disease and the response to treatment. There is no comparison (control) group of patients.

See study checklist.

A systematic process for setting and monitoring standards of clinical care. Whereas ‘guidelines’ define what the best clinical practice should be, ‘audit’ investigates whether best practice is being carried out. Clinical audit can be described as a cycle or spiral. Within the cycle there are stages that follow a systematic process of establishing best practice, measuring care against specific criteria, taking action to improve care, and monitoring to sustain improvement. The spiral suggests that as the process continues, each cycle aspires to a higher level of quality.

The extent to which a specific treatment or intervention, when used under usual or everyday conditions, has a beneficial effect on the course or outcome of disease compared with no treatment or other routine care. (Clinical trials that assess effectiveness are sometimes called management trials.) Clinical ‘effectiveness’ is not the same as efficacy.

The importance of a particular guideline recommendation to the clinical management of the target population.

A term sometimes used in guideline development work to refer to the questions about treatment and care that are formulated in order to guide the search for research evidence. When a clinical question is formulated in a precise way, it is called a focused question.

A research study conducted to compare the effects of two or more healthcare interventions, for example a trial conducted to assess the effectiveness and safety of a new cancer drug compared with the old treatment. Each trial is designed to answer scientific questions and find better ways to treat individuals with a specific disease. This general term encompasses controlled clinical trials and randomised controlled trials.

A healthcare professional providing patient care, for example doctor, nurse, physiotherapist.

A group of patients, rather than an individual, used as the basic unit for investigation. They might be families, schools, medical practices or whole communities. See also cluster randomised trial.

A trial in which groups of individuals or clusters (e.g. patients in a GP surgery or people living in a community) are randomly allocated to treatment groups. It is usually carried out to evaluate the effectiveness of an intervention provided at the community level. Take, for example, a smoking cessation study of two different interventions – leaflets and teaching sessions. Each GP surgery within the study would be randomly allocated to administer one of the two interventions. See also cluster.

An international, non-profit, independent organisation that maintains up-to-date information about healthcare interventions by producing and disseminating systematic reviews of their effectiveness. The Cochrane Database of Systematic Reviews contains regularly updated reviews on a variety of health issues and is available electronically as part of the Cochrane Library.

A regularly updated collection of evidence-based medicine databases including the Cochrane Database of Systematic Reviews (reviews of randomised controlled trials prepared by the Cochrane Collaboration). The Cochrane Library is available on CD-ROM and the internet.

A condition in which the small intestine absorptive surface is damaged owing to an intolerance to gluten. It may lead to impaired digestion and absorption of foods and may be associated with diarrhoea.

A group of people sharing some common characteristic or exposure (e.g. people working in a specific environment or patients with the same disease) within a specified period of time.

A type of observational study that takes a group (cohort) of people and follows their progress over time in order to measure outcomes such as disease or mortality rates and make comparisons according to the type of exposure (treatments or interventions) that they received. For example, comparing mortality between one group of patients that received a specific treatment and one group which did not (or between two groups that received different levels of treatment). Cohorts can be assembled in the present and followed into the future (a ‘concurrent’ or ‘prospective’ cohort study) or identified from past records and followed forward from that time up to the present (a ‘historical’ or ‘retrospective’ cohort study).

Substances that do not dissolve into a true solution and do not pass through a semi-permeable membrane. Colloid solutions tend to remain in the intravascular compartment (within the circulation) longer than crystalloid solutions, and so a smaller amount may be needed to maintain an adequate intravascular volume. Colloids also increase colloidal osmotic pressure, and so draw water from the interstitial spaces into the intravascular compartment. However, when capillary permeability is increased, colloids may leak across the capillary membrane and increase interstitial oncotic pressure, causing oedema. This may also happen if too much colloid is given. Types of colloids include dextran and gelatin (e.g. Gelofusine® and Haemaccel®).

A statistical technique used to express uncertainty about the findings from a study or group of studies. A confidence interval describes a range of possible effects (of a treatment or intervention) that are consistent with the results of a study or group of studies. A wide confidence interval indicates a lack of certainty or precision about the true size of the clinical effect and is seen in studies with too few patients. Where confidence intervals are narrow they indicate more precise estimates of effects and a larger sample of patients studied. It is usual to interpret a ‘95%’ confidence interval as the range of effects within which we are 95% confident that the true effect lies.

The process of ensuring that the researcher entering new participants in a randomised controlled trial is unaware of the group (intervention or control) the participants have been allocated/assigned to. This is distinct from blinding and is done to prevent selection bias.

A factor or a variable that can distort the true relationship between the exposure/risk factor and outcome in a study and can contribute to misleading findings if it is not understood or appropriately dealt with. It is an important cause of bias in study results and can be dealt with during the stage of study design or data analysis or both. For example, if a group of people exercising regularly and a group of people who do not exercise have an important age difference then any difference found in outcomes about heart disease could well be due to one group being older than the other rather than due to the exercising. Age is the confounding factor here and the effect of exercising on heart disease cannot be assessed without adjusting for age differences in some way.

A variety of techniques that aim to reach an agreement on a particular issue. In the development of clinical guidelines, consensus methods may be used where there is a lack of strong research evidence on a particular topic.

A condition in which passing faeces occurs infrequently, or with difficulty.

In a controlled trial it refers to a group of participants recruited to act as a comparator for one or more healthcare intervention. This group may receive no healthcare intervention, continue standard treatment or receive a placebo (dummy treatment) in order to provide a comparison for a group receiving an experimental intervention, such as a new drug. It is also known as a comparison group.

A clinical trial testing a specific drug or other treatment involving two (or more) groups of patients with the same disease. One (the experimental group) receives the treatment that is being tested, and the other (the comparison or control group) receives an alternative treatment, a placebo (dummy treatment) or no treatment. The two groups are followed up to compare differences in outcomes to see how effective the experimental treatment was. A CCT where patients are randomly allocated to treatment and comparison groups is called a randomised controlled trial.

A type of economic evaluation where both costs and benefits of healthcare treatment are measured in the same monetary units. If benefits exceed costs, the evaluation would recommend providing the treatment.

Value for money. A specific healthcare treatment is said to be ‘cost-effective’ if it gives a greater health gain than could be achieved by using the resources in other ways.

A type of economic evaluation comparing the costs and the effects on health of different treatments. Health effects are measured in ‘health-related units’, for example, the cost of preventing one additional heart attack.

A special form of cost-effectiveness analysis where health effects are measured in quality-adjusted life years (QALYs). A treatment is assessed in terms of its ability to both extend life and to improve the quality of life.

A form of chronic inflammatory bowel disease.

A type of observational study where information is collected from a defined set of people at a single point in time or time period – a snapshot. (This type of study contrasts with a longitudinal study, which follows the same set of people over a period of time.)

Substances that form a true solution and pass freely through a semi-permeable membrane. They contain water and electrolytes and stay in the intravascular compartment for a shorter time than colloids. Around 2–3 times more crystalloid than colloid is needed to achieve an equivalent haemodynamic response. Crystalloids are useful in maintaining fluid balance. The type of crystalloid given as fluid maintenance needs to be tailored to the need of the patient and has to take into account the daily requirement, insensible losses and measured losses of fluid and electrolytes. Types of crystalloid include normal saline, dextrose 5% and Hartmann’s solution (sodium lactate).

A drug that damages or destroys cells.

Decision analysis is the study of how people make decisions or how they should make decisions. There are several methods that decision analysts use to help people to make better decisions, including decision trees.

A decision tree is a method for helping people to make better decisions in situations of uncertainty. It illustrates the decision as a succession of possible actions and outcomes. It consists of the probabilities, costs and health consequences associated with each option. The overall effectiveness or overall cost-effectiveness of different actions can then be compared.

A process by which members of a working group or committee ‘declare’ any personal or professional involvement with a company (or related to a technology) that might affect their objectivity, for example if their position or department is funded by a pharmaceutical company.

A state arising from loss of extracellular fluids and/or intracellular fluid.

A study to assess the effectiveness of a test or measurement in terms of its ability to accurately detect or exclude a specific disease, rather than to assess patient-related outcomes. The accuracy of the test is compared with some method (which is also known as the reference standard) of determining the true disease status.

A term used in health economics describing when an option for treatment is both less clinically effective and more costly than an alternative option. The less effective and more costly option is said to be ‘dominated’.

A study in which neither the subject (patient) nor the observer (investigator/clinician) is aware of which treatment or intervention the subject is receiving. The purpose of blinding is to protect against bias.

An infection of the intestinal tract that causes diarrhoea with blood and mucus.

Pain on passing urine.

A comparison of alternative courses of action in terms of both their costs and consequences. In health economic evaluations, the consequences should include health outcomes.

See clinical effectiveness.

The extent to which a specific treatment or intervention has a beneficial effect on the course or outcome of disease compared with no treatment or other routine care under controlled clinical conditions, for example in a laboratory.

Clinical procedures that are regarded as advantageous to the patient but not urgent.

Diseases that are present in or peculiar to particular localities or populations.

Infection of the intestine.

The study of diseases within a population, covering the causes and means of prevention.

A measure of the settling of red blood cells in a tube of blood during 1 hour. The rate is an indication of inflammation and increases in many diseases.

Evidence-based clinical practice involves making decisions about the care of individual patients based on the best research evidence available rather than basing decisions on personal opinions or common practice (which may not always be evidence based). Evidence-based clinical practice therefore involves integrating individual clinical expertise and patient preferences with the best available evidence from research.

A code (e.g. 1++, 1+) linked to an individual study, indicating where it fits into the hierarchy of evidence and how well it has adhered to recognised research principles. Also called level of evidence.

A table summarising the results of a collection of studies which, taken together, represent the evidence supporting a particular recommendation or series of recommendations in a guideline.

See selection criteria.

A research study designed to test whether a treatment or intervention has an effect on the course or outcome of a condition or disease, where the conditions of testing are to some extent under the control of the investigator. Also known as an intervention study. Controlled clinical trials and randomised controlled trials are examples of experimental studies.

A treatment or intervention (e.g. a new drug) being studied to see whether it has an effect on the course or outcome of a condition or disease.

The degree to which the results of a study hold true in non-study situations, for example in routine clinical practice. May also be referred to as the generalisability or applicability of study results to non-study patients or populations.

A study question that clearly identifies all aspects of the topic that are to be considered while seeking an answer. Questions are normally expected to identify the patients or population involved, the treatment or intervention to be investigated, what outcomes are to be considered, and any comparisons that are to be made. For example, do insulin pumps (intervention) improve blood sugar control (outcome) in adolescents with type 1 diabetes (population) compared with multiple insulin injections (comparison)? See also clinical question.

A graphical display of results from individual studies included in a meta-analysis together with the pooled meta-analysis result. This allows visual comparison of results from individual studies and examination of the degree of heterogeneity between studies.

A transient disorder due to enteric infection and characterised by the sudden onset of diarrhoea with or without vomiting.

The extent to which the results of a study hold true for a population of patients beyond those who participated in the research. See also external validity.

A method, procedure or measurement that is widely accepted as being the best available, against which new developments should be compared.

Reports that are unpublished or have limited distribution, and are not included in easily accessible bibliographic retrieval system (such as journals or databases).

A systematically developed tool that describes aspects of a patient’s condition and the care to be given. A good guideline makes recommendations about treatment and care, based on the best research available rather than on opinion. It is used to assist clinician and patient decision making about appropriate health care for specific clinical conditions.

Course of action advised by the Guideline Development Group on the basis of their assessment of the supporting evidence.

A branch of economics that studies decisions about the use and distribution of healthcare resources.

Health technologies include medicines, medical devices such as artificial hip joints, diagnostic techniques, surgical procedures, health promotion activities (e.g. the role of diet versus medicines in disease management) and other therapeutic interventions.

The process of determining the clinical and cost-effectiveness of a health technology undertaken by NICE to provide patients, healthcare professionals and managers with an authoritative source of advice on new and existing health technologies.

Abnormal enlargement of both the liver and the spleen.

In the general sense, the term is used to describe variation in the participants, interventions and outcomes across a set of studies. Statistical heterogeneity is the term used in meta-analyses and systematic reviews to describe variation in the results or estimates of effects beyond the amount expected solely due to chance. It is the opposite of homogeneity.

An established hierarchy of study types, based on the degree of certainty that can be attributed to the conclusions drawn from a well-conducted study. A systematic review of good-quality randomised controlled trials (RCTs) with homogeneity in their results (which are statistically significant) is at the top of this hierarchy. Well-conducted studies of patients’ views and experiences would appear at a lower level in the hierarchy of evidence.

In the general sense, the term is used to imply similarity in the participants, interventions and outcomes across a set of studies. Statistical homogeneity means that the results of studies or estimates of effects included in a systematic review or meta-analysis are similar or they do not vary beyond the amount expected by chance. It is the opposite of heterogeneity.

An electrolyte and acid/base disturbance that may arise as a consequence of infusing large quantities of chloride-containing solutions, such as 0.9% normal saline.

An abnormally high level of glucose in the bloodstream.

An electrolyte disturbance in which the plasma potassium concentration is greater than 5.5 mmol/l.

An electrolyte disturbance in which the plasma sodium concentration is greater than 145 mmol/l. In severe hypernatraemia (e.g. plasma sodium levels more than 160 mmol/l), there are risks associated with a sudden fall in plasma sodium level during rehydration, and such patients require a modified approach to their fluid management.

Overactive or overresponsive reflexes.

Abnormally high muscle tension.

An abnormally low level of glucose in the bloodstream.

An electrolyte disturbance in which the plasma sodium concentration is less than 135 mmol/l.

A state of decreased blood volume or more specifically of blood plasma volume that results in inadequate circulation of blood to the body tissues.

A quantitative measure of statistical heterogeneity which describes the percentage of variability in the study results or effects of estimates that is beyond the amount expected by chance. Generally, a value greater than 50% is considered to represent substantial heterogeneity.

A congenital or acquired condition in which the immune system is functionally impaired, resulting in an increased risk of infection.

Incidence and prevalence are tools to describe how common a disease or an event/outcome is with reference to the size of population. Incidence measures the frequency of disease or an event/outcome in new cases only. The two commonly used measures of incidence are the risk or absolute risk and the rate.

See selection criteria.

A qualitative research technique. It is a face-to-face conversation between a researcher and a respondent with the purpose of exploring issues or topics in detail. It does not use pre-set questions, but is shaped by a defined set of topics or issues.

A child younger than 1 year.

A group of chronic intestinal diseases characterised by inflammation of the gastrointestinal tract. The two most common types of inflammatory bowel disease are Crohn’s disease and ulcerative colitis.

A strategy used in randomised controlled trials whereby data from study participants are analysed according to the group to which they were initially randomly allocated, regardless of whether or not they had dropped out, fully complied with the treatment, or crossed over and received the alternative treatment. Intention-to-treat analyses are favoured in assessments of clinical effectiveness as they mirror the non-compliance and treatment changes that are likely to occur when the treatment is used in practice.

Refers to the integrity of the study design or the extent to which the study design was successful in preventing bias. See also methodological quality.

Healthcare action intended to benefit the patient, for example drug treatment, surgical procedure, psychological therapy, etc.

A group of participants in a study who receive a specific healthcare intervention. See also control group.

A blockage of the intestine typically resulting in symptoms such as abdominal pain and vomiting.

The administration of fluids directly into the venous circulation.

A condition in which a part of the intestine prolapses (telescopes) into another immediately adjacent section of the intestine, typically resulting in symptoms of intestinal obstruction. It can lead to gangrene of the affected gut segment.

A state of severe protein malnutrition marked by lethargy, growth restriction, anaemia, oedema, potbelly, skin depigmentation, and hair loss or change in hair colour.

See evidence level.

An abnormally high level of white cells (leucocytes) in the blood.

A survey method of measuring attitudes that asks respondents to specify their level of agreement with a statement.

A process of collecting, reading and assessing the quality of published (and unpublished) articles on a given topic.

A type of observational study that follows a group of people at more than one point in time or where repeated observations are made. (This type of study contrasts with a cross-sectional study, which observes a defined set of people at a single point in time.)

The reduced absorption of one or more substances by the small intestine.

See blinding.

A method to minimise bias in a case–control study whereby people in the control group are selected if they have particular attributes (e.g. age, sex) similar to those of the individual cases.

Also known as the average value, it is calculated by dividing the sum of all the observations by the number of observations.

A method used in meta-analysis to combine (or pool) the outcomes measured in a continuous scale (e.g. weight, age). The results of each study included in the meta-analysis are given a weight depending on the influence it has on the overall pooled results or the precision of its effect estimate. This is different from the standardised mean difference (SMD).

A statistical technique used in a systematic review to combine (pool) the results from a collection of independent studies into a single estimate of a treatment effect. Where studies are not compatible, for example because of differences in the study populations or in the outcomes measured, it may be inappropriate or even misleading to statistically pool results in this way. See also systematic review and heterogeneity.

The overall approach of a research project, for example the study will be a randomised controlled trial, of 200 people, over 1 year.

The extent to which a study has conformed to recognised good practice in the design and execution of its research methods. Also known as study quality. See also internal validity.

A therapeutic agent that protects the lining (mucosa) of the gut.

A study where subjects are selected from different geographical locations or sites, for example a cooperative study between different hospitals or an international collaboration involving patients from more than one country.

Leads and contributes to improved, safe patient care by informing, supporting and influencing the health sector.

A measure used to give an informative value of a test result and which is calculated as the ratio between 1 − sensitivity and specificity. It is used to describe how much to decrease the probability of a disease if the test is negative (or rule out a disease). The lower the negative likelihood ratio (less than 1) for a test result, the less the likelihood of the disease.

In diagnostic testing, this expresses the probability that someone with a negative test result does not have the condition of interest.

A service that provides 24 hour confidential health advice and information. NHS Direct can help people who are feeling ill, are unsure what to do, would like to find out more about a condition or treatment, or need details of local health services. The service can be accessed by visiting www.nhsdirect.nhs.uk, going to NHS Direct Interactive on digital satellite TV (by pressing the interactive button on the remote control) or by calling 0845 4647.

Number needed to harm. See number needed to treat.

See number needed to treat.

See observational study.

This measures the impact of a treatment or intervention. It states how many patients need to be treated with the treatment in question in order for one patient to get a beneficial outcome or prevent an adverse outcome For example, if the NNT = 4, then four patients would have to be treated to prevent one bad outcome. The closer the NNT is to 1, the better the treatment is. Analogous to the NNT is the number needed to harm (NNH), which is the number of patients that would need to receive a treatment to cause one additional adverse event. For example, if the NNH = 4, then four patients would have to be treated for one bad outcome to occur.

A physical or biological measurement that follows a standardised procedure and is less open to subjective interpretation by potentially biased observers and study participants.

In research, this refers to a study in which nature is allowed to take its course and the investigator simply observes what is happening. Also known as a non- experimental study. Changes or differences in one characteristic (e.g. whether or not people received a specific treatment or intervention) are studied in relation to changes or differences in other(s) (e.g. whether or not they died), without the intervention of the investigator. There is a greater risk of selection bias than in experimental studies. There are various types of observational studies, such as cohort study, case–control study, cross-sectional study and case series.

Odds are a way of representing probability, especially familiar for betting. It is calculated by dividing the number of people with a defined outcome or event in a given sample of population with the number of people who did not have that outcome or event.

The ratio of the odds of an outcome in one group of people to the odds in another group of people. In recent years odds ratios have become widely used in reports of clinical studies. They provide an estimate (usually with a confidence interval) for the effect of a treatment. An odds ratio of 1 between two treatment groups for a specific outcome would imply that the risk of that outcome is the same in each group. For rare events the odds ratio and the relative risk (which uses actual risks and not odds) will be very similar. See also relative risk or risk ratio (RR).

Specially constituted fluid containing as essential ingredients an organic solute (e.g. a carbohydrate or amino acid) and sodium chloride. Such organic solutes are subject to active intestinal co-transport (absorption) with sodium and so enhance salt and hence water absorption. Most ORS solutions contain glucose as the organic solute.

The administration of fluids by mouth or via nasogastric tube.

Osmotic concentration.

The movement of solvent molecules across a membrane to an area where there is a higher concentration of solute to which the membrane is impermeable.

The end result of care and treatment and/ or rehabilitation. In other words, the change in health, functional ability, symptoms or situation of a person, which can be used to measure the effectiveness of care/treatment/rehabilitation. Researchers should decide what outcomes to measure before a study begins; outcomes are then assessed at the end of the study.

A functional obstruction of the ileum (bowel) due to loss of intestinal movement.

An organism that obtains food and shelter from another organism.

See primary care trust.

Review of a study, service or recommendations by those with similar interests and expertise to the people who produced the study findings or recommendations. Peer reviewers can include professional and/or patient/carer representatives.

Inflammation of a vein.

An abnormal intolerance to light.

Placebos are fake or inactive treatments received by participants allocated to the control group in a clinical trial and which are indistinguishable from the active treatments being given in the experimental group. They are used so that participants are ignorant of their treatment allocation in order to be able to quantify the effect of the experimental treatment over and above any placebo effect due to receiving care or attention.

The best single estimate for the true value of a treatment effect or other measurement obtained from a research study. For example, researchers in one clinical trial take their results as their best estimate of the real treatment effect for the population from which the study sample was selected – this is their estimate at their point in time. The precision or accuracy of the estimate is measured by a confidence interval.

A measure used to give an informative value of a test result and which is calculated as the ratio between sensitivity and 1 – specificity. It is used to describe how much to increase the probability of a disease if the test is positive (or rule in a disease). The higher the positive likelihood ratio (more than 1) for a test result, the greater the likelihood of the disease.

In diagnostic testing, this expresses the probability that someone with a positive test result does have the condition of interest.

See statistical power.

Prevalence and incidence are tools to describe how common a disease or an event/outcome is with reference to the size of population. Prevalence is the proportion of people in a defined population that have the disease or an event/ outcome at a specific time. In contrast to incidence, which quantifies disease frequency among new cases only, prevalence measures disease frequency in both old and new cases (all existing cases) at a particular time.

Health care delivered to patients outside hospitals. Primary care covers a range of services provided by GPs, nurses and other healthcare professionals, dentists, pharmacists and opticians.

An NHS organisation responsible for improving the health of local people, developing services provided by local GPs and their teams (called primary care) and making sure that other appropriate health services are in place to meet local people’s needs.

An outcome deemed a priori to be of greatest importance at the start of a research study.

How likely an event is to occur, for example how likely a treatment or intervention will alleviate a symptom.

A live microbial food which is intended to have beneficial effects by improving the intestinal microbial balance of the host.

Patient or disease characteristics, for example age or comorbidity, that influence the course of the disease under study. In a randomised trial to compare two treatments, chance imbalances in variables (prognostic factors) that influence patient outcome are possible, especially if the size of the study is fairly small. In terms of analysis, these prognostic factors become confounding factors.

A study in which people are entered into the research and then followed up over a period of time with future events recorded as they happen. This contrasts with studies that are retrospective.

A plan or set of steps that defines appropriate action. A research protocol sets out, in advance of carrying out the study, what question is to be answered and how information will be collected and analysed. Guideline implementation protocols set out how guideline recommendations will be used in practice by the NHS, both at national and local levels.

If a study is done to compare two treatments then the P value is the probability of obtaining the results of that study, or something more extreme, if there really was no difference between treatments. (The assumption that there really is no difference between treatments is called the ‘null hypothesis’.) Suppose the P value was P = 0.03. What this means is that if there really was no difference between treatments then there would only be a 3% chance of getting the kind of results obtained. Since this chance seems quite low we should question the validity of the assumption that there really is no difference between treatments. We would conclude that there probably is a difference between treatments. By convention, where the value of P is below 0.05 (i.e. less than 5%) the result is considered to be statistically significant.

Narrowing of the stomach outlet so that food cannot pass easily from it into the intestine. This condition is usually seen in young infants, and is associated with persistent vomiting.

Qualitative research is used to explore and understand people’s beliefs, experiences, attitudes, behaviour and interactions. It generates non-numerical data, for example a patient’s description of their pain rather than a measure of pain. In health care, qualitative techniques have been commonly used in research documenting the experience of chronic illness and in studies about the functioning of organisations. Qualitative research techniques such as focus groups and in-depth interviews have been used in one-off projects commissioned by guideline development groups to find out more about the views and experiences of patients and carers.

A measure of health outcome which looks at both length of life and quality of life. QALYs are calculated by estimating the years of life remaining for a patient following a particular care pathway and weighting each year with a quality of life score (on a 0 to 1 scale). 1 QALY is equal to 1 year of life in perfect health, or 2 years at 50% health, and so on.

Research that generates numerical data or data that can be converted into numbers, for example clinical trials or the national Census that counts people and households.

A method of assigning or allocating participants in an experimental study whereby the assignment of patients to treatment and comparison groups is not done randomly, or patients are not given equal probabilities of selection. For example, participants may be assigned to the groups based on their date of birth or day of the week or every alternate person. These methods lead to selection bias in a study. See also random allocation.

A method that uses the play of chance to assign participants or units to comparison groups in an experimental study, for example by using a random numbers table or a computer-generated random sequence. Random allocation implies that each individual (or each unit in the case of cluster randomisation) being entered into a study has the same chance of receiving each of the possible interventions. See also quasi-random allocation.

The process of randomly allocating participants into comparison groups in a controlled trial. The aim of this process is to ensure that the experimental and the control groups are similar with respect to all potential confounding variables except the treatment or intervention being investigated.

An experimental study to test a specific drug or other treatment in which people are randomly allocated to two (or more) groups: one (the intervention or experimental group) receiving the treatment that is being tested, and the other (the comparison or control group) receiving an alternative treatment, a placebo (dummy treatment) or no treatment. The two groups are followed up to compare differences in outcomes to see how effective the experimental treatment was.

A curve representing the relationship between sensitivity (true positive fraction and 1 – specificity (false positive fraction) in the case of a continous test result. It displays the trade-offs between sensitivity and specificity when the cut-off value for a positive test result is varied. The measure used to determine the overall accuracy of a test using the ROC curve is known as the area under ROC curve (AROC). In general, an AROC of 0.5–0.7 is associated with a marginally useful test, of 0.7–0.9 with a good test, and of greater than 0.9 with an excellent test.

Important symptoms or signs of dehydration whose presence is associated with a risk of progression to shock.

An assessment carried out when the patient is geographically remote from the assessor (e.g. via telephone) such that physical examination is not possible.

A statistical technique used to predict the effect or influence of one or more independent factors/variables on a dependent factor/variable, for example the effect of age, smoking and occupation on the incidence of lung cancer. Logistic regression and meta-regression are two types of regression analysis.

The ratio of the risks of a given event or outcome (e.g. an adverse reaction to the drug being tested) in one group of subjects compared with another group. When the ‘risk’ of the event is the same in the two groups, the relative risk is 1. In a study comparing two treatments, a relative risk of 2 would indicate that patients receiving one of the treatments had twice the risk of an undesirable outcome than those receiving the other treatment.

Reliability refers to a method of measurement that consistently gives the same results. For example, someone who has a high score on one occasion tends to have a high score if measured on another occasion very soon afterwards. With physical assessments it is possible for different clinicians to make independent assessments in quick succession, and if their assessments tend to agree then the method of assessment is said to be reliable.

A retrospective study deals with events or outcomes that have already occurred in the past and does not involve studying future events. This contrasts with studies that are prospective.

See absoute risk or risk.

The absolute difference between the risks of two groups. Also known as absolute risk difference.

In the UK medical/nursing world the term ‘royal colleges’, as for example in ‘The Royal College of …’, refers to organisations that usually combine an educational standards and examination role with the promotion of professional standards.

The provision of support for patients in whom the clinician has some uncertainty as to whether the patient has a self-limiting illness and is concerned that their condition may deteriorate. Safety netting may take a number of forms, such as dialogue with the patient or carer about symptoms and signs to watch for, advice about when to seek further medical attention, review after a set period, and liaising with other healthcare services.

A part of the study’s target population from which the subjects of the study will be recruited. If subjects are drawn in an unbiased way from a particular population, the results can be generalised from the sample to the population as a whole.

SIGN was established in 1993 to sponsor and support the development of evidence- based clinical guidelines for the NHS in Scotland.

Care provided in hospitals.

An outcome deemed a priori as less important than the primary outcome and is measured to evaluate additional effects of the intervention.

A type of bias that occurs if:

• the characteristics of the sample differ from those of the wider population from which the sample has been drawn, or
• there are systematic differences between comparison groups in a study in terms of prognosis or responsiveness to treatment.

Explicit standards used by guideline development groups to decide which studies should be included and excluded from consideration as potential sources of evidence.

Structured interviews involve asking people pre-set questions. A semi-structured interview allows more flexibility than a structured interview. The interviewer asks a number of open-ended questions, following up areas of interest in response to the information given by the respondent.

In diagnostic testing, this refers to the proportion of cases with the target condition correctly identified by the diagnostic test out of all the cases that have the target condition.

A pathological condition in which there is inadequate blood perfusion of the vital organs.

A study in which either the subject (patient/participant) or the observer (clinician/ investigator) is not aware of which treatment or intervention the subject is receiving.

A term used to describe a physical characteristic of the skin. In patients with clinical dehydration, skin turgor may be reduced, so that when a fold of skin is gently pinched and then released it fails to immediately retract in the normal way, but rather retains a ridged appearance for a variable period owing to a reduction in its fluid content.

In diagnostic testing, this refers to the proportion of cases without the target condition correctly identified by the diagnostic test out of all the cases that do not have the target condition.

A measure of the spread, scatter or dispersion of a set of measurements. Usually used along with the mean (average) to describe numerical data.

The difference in the means divided by a standard deviation. This standard deviation is the pooled standard deviation of participants’ outcomes across the whole trial. An important differerence from the weighted mean difference (WMD) is that the value of the SMD is not dependent on the measurement scale or unit, for example different trials may be assessing the same outcome (such as weight) but using different scales/units for measuring it (such as kilograms or ounces).

The ability of a study to demonstrate a statistically significant result (association or difference between two variables) given that such a result exists in the population from which the sample was recruited. For example, 80% power in a clinical trial means that the study has an 80% chance of ending up with a P value of less than 5% in a statistical test (i.e. a statistically significant treatment effect) if there really was an important difference (e.g. 10% versus 5% mortality) between treatments. If the statistical power of a study is low, the study results will be questionable (the study might have been too small to detect any differences). By convention, 80% is an acceptable level of power. See also P value.

A research technique where the interviewer controls the interview by adhering strictly to a questionnaire or interview schedule with pre-set questions.

A list of questions addressing the key aspects of the research methodology that must be in place if a study is to be accepted as valid. A different checklist is required for each study type. These checklists are used to ensure a degree of consistency in the way that studies are evaluated.

People who have been identified as the subjects of a study.

See methodological quality.

The kind of design used for a study. Randomised controlled trial, case–control study and cohort study are all examples of study types.

A person who takes part in an experiment or research study.

A study in which information is systematically collected from people (usually from a sample within a defined population).

See bias.

A study with a clearly formulated question that uses systematic and explicit methods with predetermined criteria to identify, appraise and synthesise the results of relevant research. It may or may not include a meta-analysis to summarise the results.

Involving the whole body.

An abnormally rapid heart rate.

An abnormally rapid breathing rate.

The people to whom guideline recommendations are intended to apply. Recommendations may be less valid if applied to a population with different characteristics from the participants in the research study, for example in terms of age, disease state or social background.

A major medical centre providing complex treatments that receives referrals from both primary and secondary care. Sometimes called a tertiary referral centre. See also primary care and secondary care.

A state of acute shock, due to septicaemia, that can be life-threatening if not treated.

A study in which the statistical analysis is carried out without knowing which treatment patients received, in addition to the patients and investigators/ clinicians being unaware which treatment patients were getting.

A trust is an NHS organisation responsible for providing a group of healthcare services. An acute trust provides hospital services. A mental health trust provides most mental health services. A primary care trust buys hospital care on behalf of the local population, as well as being responsible for the provision of community health services.

A type of inflammatory bowel disease affecting the large intestine (colon).

An assessment of how well a tool or instrument measures what it is intended to measure. See also external validity and internal validity.

A factor that differs among and between groups of people. It includes participant characteristics (such as age or sex) or measurements (such as blood pressure or heart rate) or treatments (such as drugs).

See mean difference or weighted mean difference (WMD).