Issues of design and methodology in long-term followup studies.

Beginning with Vaillant, followup studies of schizophrenia have devoted increasing attention to issues of design and methodology. The major advances and elements are described here and include: (1) conceptual framework, (2) design, (3) sample representativeness, (4) sample description, (5) data source and quality, (6) measures, (7) reliability, (8) diagnosis, (9) comparison groups, (10) assessment independence, (11) outcome, (12) missing subjects/bias testing, and (13) statistical techniques.