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longitudinal study[‚län·jə‚tüd·ən·əl ′stəd·ē]
longitudinal studyan investigation which involves making observations of the same group at sequential time intervals. Thus, a longitudinal study of a COHORT of children may be made to assess, for example, the effect of social class on school achievement (see BIRTH COHORT STUDY). Longitudinal studies are used by the National Children's Bureau to document various aspects of children's development in the UK. However, longitudinal studies are not only appropriate for studying human development or change, they may also be used to observe change over time within organizations.
The advantage of longitudinal studies compared with CROSS-SECTIONAL STUDIES is that the causal factor involved in a sequence of changes an be directly explored using data collected before and after changes (e.g. analysis of the effect of changes in the school curriculum). The main disadvantages are the greater expense of repeated study, the possible HAWTHORNE EFFECT of repeated studies and the influence of other changes which may be occurring concurrently (e.g. changes in the school curriculum may take place at the same time as changes in the resourcing of educational services). Compare PANEL STUDY.