Controlled Time Series Design
Data are collected at several times both before and after the intervention in the intervention group and at the same times in a control group. Data collected before the intervention allow the underlying trend and cyclical (seasonal) effects to be estimated. Data collected after the intervention allow the intervention effect to be estimated while accounting for underlying secular trends. Use of a control group addresses the greatest threat to the validity of a time series–design which is the occurrence of another event at the same time as the intervention, both of which may be associated with the outcome.