From Paul Clark
Robert Matthews describes a means of estimating an unknown total population
by capturing, releasing and then capturing again a sample of that population
(“Hidden truths”, 23 May, p 28).
He states that the proportion of recaptured
individuals in the second set gives an estimate of overall numbers. The smaller
the proportion recaptured, the larger the population is likely to be.
However, it seems this method relies on the assumption that each individual
has an equal chance of being recaptured. Is it not likely that there will be a
range of abilities when it comes to avoiding capture? Less adept individuals
could therefore be expected to be over-represented in the second captured sample
and would tend to give an underestimate of the overall population.
paul.clark@kent.gov.uk
