Monday, 11 July 2011

capture - recapture

an interesting use of ratios is in the 'capture-recapture' method for estimating a population size

pull out a sample
mark it in some way
put the sample back
pull out another sample and use the fraction/ratio of marked things to estimate the full population size

suppose 40 butterflies are marked in some way and released in a particular location

then a further 20 are captured as shown:

how many butterflies would you estimate there to be from this information?

this program enables repeated capturing

repeatedly making second captures enables a comparison of different estimates, exploring the variation:
what are the extremes and what is the mean?

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