Birth  Embryology Statistics
 confidence interval  An interval describing the range of values within which there is reasonable certainty that the true effect lies. Uncertainty increases with the width of the interval.
 double blind study  A statistical study in which neither the subject nor the observer is aware of which treatment or intervention the subject is receiving in order to protect against bias.
 epidemiology  The statistical study of diseases within a population, covering the causes and means of prevention.
 incidence  rate of new (newly diagnosed) cases of the disease, reported as the number of new cases occurring within a period of time. This can also be further categorized by different subsets of the population; gender, racial origin, age group or by diagnostic category.
 KaplanMeier  commonly used statistical probability of survival (lifetable) method used in medicine. Data requires both the time of commencement of the treatment and the time the measured event occurred (death, relapse, hospitalization).
 mean difference  the absolute difference between the mean value in two groups in a clinical trial, which estimates the amount by which the intervention changes the outcome on average compared with the control.
 meta analysis  The pooled results from a collection of independent statistical studies to merge their findings into a single estimate of a treatment effect. Note depending upon the individual studies criteria it may be inappropriate or misleading to statistically pool results in this way.
 multi centre study  A statistical study where subjects are selected from different locations or populations.
 odds ratio  the ratio of the likelihood of an event occurring in one group to that of it occurring in another group. An odds ratio of 1 indicates that the condition or event under study is equally likely to occur in both groups. An odds ratio greater than 1 indicates that the condition or event is more likely to occur in the rst group and an odds ratio less than 1 indicates that the condition or event is less likely to occur in the first group.
 outcome reporting bias  the selective reporting of some outcomes but not others. Outcomes with favourable ndings may be reported more. For example, adverse events have been found to be reported more often in unpublished studies. This may result in more favourable results for published studies.
 prevalence  actual number of cases alive, with the disease either during a period of time (period) or at a particular date in time (point), reported as the number of cases as a fraction of the total population at risk. This can also be further categorized by different subsets of the population; gender, racial origin, age group or by diagnostic category.
 prospective study  A statistical 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.
 randomised controlled trial  a study in which participants are allocated at random to receive one of several clinical interventions. One of these interventions is the standard of comparison or control. The control may be a standard practice, a placebo or no intervention at all.
 relative risk  the ratio of the risk (rate) of an outcome in an exposed group (eg to a specific medicine) to the risk (rate) of the outcome in an unexposed group in a specifed time period
 retrospective study  A statistical study of the present and past and does not involve studying future events.
 sensitivity  the proportion of people with the condition who have a positive test result.
 (Some terms based upon Glossary in NICE Guidelines, No. 13 Bookshelf).
