TY  - RPRT
TI  - Statistics notebook: entry II.B: Observational study, (1) retrospective study, and (2) prospective study.
AU  - P N de Land
AU  - W W Chase
PY  - 1991
DO  - 10.1097/00006324-199102000-00012
UR  - https://pubmed.ncbi.nlm.nih.gov/2027656/
ID  - 2027656
ER  -