TY  - RPRT
TI  - When is a cluster?
AU  - J Berger
AU  - A Manz
PY  - 1993
DO  - 10.1016/0140-6736(93)92690-u
UR  - https://pubmed.ncbi.nlm.nih.gov/8104267/
ID  - 8104267
ER  -