A "time series" is an epidemiological research design in which a single population group of defined size is studied over a period during which preventive or therapeutic interventions take place, with measurements of factors and variables of interest at specified time intervals. The aim is to detect trends such as variations in incidence rates of disease or other health-related phenomena in response to particular interventions. It may be a simple pre-test/post-test design, or an interrupted time series, in which several measurements are made both before and after an intervention; the latter is regarded as the more valid of these methods.

JOHN M. LAST

(SEE ALSO: Cohort Study; Epidemiology; Observational Studies)