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Capture recapture is used when a population is too large or hidden to count directly. You take a first sample, mark it, release it, then later take a second sample and see how many marked individuals are found again.
The population is the whole group you want to estimate, and a sample is a smaller group taken from it. The key idea is that the proportion marked in the second sample should reflect the proportion marked in the whole population.
If only a few of the second sample are marked, the total population is probably large. If many are marked, the total population is probably smaller.
Question 1
3 marksBhavna has a bag containing a large number of beads.
She wants to find an estimate for the number of beads in the bag.
Bhavna takes a sample of 30 beads from the bag.
She marks each bead with a black cross.
She then puts the beads back in the bag.
Bhavna shakes the bag.
She now takes another sample of 30 beads from the bag.
4 of these beads have been marked with a black cross.
What is capture recapture used to estimate?
Revision notes for Edexcel GCSE Maths Capture Recapture. Open the guide for explanations and worked examples. Written against the Edexcel GCSE Maths (1MA1) specification, so the content matches what's examinable rather than general Maths background.
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A wildlife worker marks 30 birds and releases them. Later, a sample of 20 birds contains 5 marked birds. Estimate the total bird population.
