Capture-recapture methods have been advocated for use in estimating completeness of a register. These methods were originally developed to estimate the size of a closed animal population. The procedure is that at one time as many animals as possible in an area are captured, tagged and released—the 'capture' stage.

What is the capture and recapture method?

The method involves capturing a number of animals, marking them, releasing them back into the population, and then determining the ratio of marked to unmarked animals in the population.

What are the advantages and disadvantages of the capture mark-recapture method?

They offer the advantage that accuracy does not depend on an assessment of the amount of habitat; their disadvantage is that accuracy does depend on capturing a large proportion of the population.