TY  - RPRT
TI  - Observational studies for intervention assessment.
AU  - H Comber
AU  - I J Perry
PY  - 2001
DO  - 10.1016/s0140-6736(00)05219-3
UR  - https://pubmed.ncbi.nlm.nih.gov/11467302/
ID  - 11467302
ER  -