A time-lag study examines the responses of different participants of similar age at different points in time. Time-lag is one of the three methods used to study developmental and generational change. The other two methods are a cross-sectional study (which examines participants of different ages at one point in time) and a longitudinal study (which examines the same participants as they age). This entry first examines the types of differences these methods assess; then, it describes the possible confounds and the procedures to follow to perform a time-lag study. Last, this entry briefly discusses the future of time-lag studies.