L'Abbé plot: A plot often used in the meta-analysis of clinical trials where the outcome is a binary variable. The event risk (number of events/number of patients in a group) in a each treatment group is plotted against the risk for the controls for each selected study. If the studies are relatively homogeneous, then the points will form a ‘cloud’ close to a line, the gradient of which will correspond to the pooled treatment effect. Large deviations or scatter indicates possible heterogeneity amongst the effect sizes from the different trials. Figure 52 shows an example. [Annals of Internal Medicine, 1987, 107, 224–33.]

Landmark analysis: A term applied to a form of analysis occasionally applied to survival time data in which a test is used to assess whether treatment predicts subsequent survival among subjects who survive to a landmark time (e.g. 6 months post-randomization) and who have, at this time, a common prophylaxis status and history of all other covariates. [Statistics in Medicine, 1996, 15, 2797–812.]

Large sample method: Any statistical method based on an approximation to a normal distribution or other probability distribution that becomes more accurate as sample size increases. See also asymptotic distribution.

Large simple trials (LST): Clinical trials in which exceptionally large numbers of patients with minimally restrictive entry criteria are used and data are collected only on essential baseline characteristics and outcomes. Such a trial allows unprecedented discretion by both patients and clinicians; patients are randomized to a study treatment, but the rest of their care is left in their own hands.