TY  - RPRT
TI  - Difficulties in evaluating non-randomized studies.
AU  - R Arriagada
AU  - A Auquier
PY  - 1989
DO  - 10.1016/0167-8140(89)90099-6
UR  - https://pubmed.ncbi.nlm.nih.gov/2672123/
ID  - 2672123
ER  -