TY  - RPRT
TI  - Ecological bias, confounding, and effect modification.
AU  - S Greenland
AU  - H Morgenstern
PY  - 1989
DO  - 10.1093/ije/18.1.269
UR  - https://pubmed.ncbi.nlm.nih.gov/2656561/
ID  - 2656561
ER  -