TY  - RPRT
TI  - Current advances in sampling theory: implications for human observational studies.
AU  - R M Royall
PY  - 1976
DO  - 10.1093/oxfordjournals.aje.a112317
UR  - https://pubmed.ncbi.nlm.nih.gov/970403/
ID  - 970403
ER  -