Page 19 - 15Diarrhoeaandvomiting

Diarrhoea and vomiting caused by gastroenteritis in children under 5 years

Malabsorption The reduced absorption of one or more substances by the small intestine.
Masking See blinding.
Matching 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.
Mean or arithmetic mean Also known as the average value, it is calculated by dividing the sum of all the
observations by the number of observations.
Mean difference or weighted A method used in meta-analysis to combine (or pool) the outcomes measured in a
mean difference (WMD) 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).
Meta-analysis 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.
Methodology The overall approach of a research project, for example the study will be a
randomised controlled trial, of 200 people, over 1 year.
Methodological quality 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.
Mucoprotective agent A therapeutic agent that protects the lining (mucosa) of the gut.
Multicentre study 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.
National Patient Safety Leads and contributes to improved, safe patient care by informing, supporting and
Agency (NPSA) influencing the health sector.
Negative likelihood ratio A measure used to give an informative value of a test result and which is
(−LR) 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.
Negative predictive value In diagnostic testing, this expresses the probability that someone with a negative
test result does not have the condition of interest.
NHS Direct 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.
NNH Number needed to harm. See number needed to treat.
NNT See number needed to treat.
Non-experimental study See observational study.
Number needed to treat This measures the impact of a treatment or intervention. It states how many patients
(NNT) 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.
Objective measure A physical or biological measurement that follows a standardised procedure
and is less open to subjective interpretation by potentially biased observers and
study participants.

xvi