A sample of n 1 animals is caught, marked, and released. Later a sample of n 2 animals is captured, of which m 2 animals have been marked. If sample size is small, the above estimator is biased.
All animals are equally likely to be captured in each sample.
Capture and marking do not affect catchability. Each sample is random. Marks are not lost between sampling occasions. All marks are recorded correctly and reported on recovery in the second sample. Individuals caught at each sample are first examined for marks, then marked and released.