IB Biology IA idea · Data science and modelling in biology

IB Biology IA idea: how good is mark and recapture? A bead-bag test

Ecologists estimate population size by marking some and catching some again. Test how accurate the method is with a population you can count.

Data science and modelling in biology
SL ideal
HL good
Simulation Modelling

By Photon Academy · Updated 13 November 2026

These ideas are starting points, not an IA to copy. Never copy an idea blindly: make the question, method and analysis your own, and check your plan with your teacher.

Example research question

To adapt, never to copy

How does the number of marked beads released (10, 25, 50, 100 and 200) affect the percent error of the Lincoln-Petersen estimate of a bag of 1000 beads, using 20 repeat samples at each level?

Change the system, the range or the method so the question is yours. Check it against the research question checklist in our Biology IA guide.

Variables

You change: number of marked individuals released, 5 or more values from 10 to 200 (in a population of known size)
You measure: percent error of the Lincoln-Petersen estimate against the true population
You keep the same: same total number of beads
same recapture sample size
random mixing
same number of repeats

Method

Use a bag of beads of known number as the population, mark some by colour, mix, draw a sample and estimate. Repeat 20 or more times at each marking level, then build a spreadsheet model to check.

Data analysis

Mean and standard deviation of percent error against marking level, box plots, comparison with a computer simulation of 1000 runs. Discuss bias.

How it works

You change Marked beads released and measure Percent error of estimate (%) in Bead population model, keeping Bag size, Sample size, Mixing method the same. Expect a graph of Error of estimate / % against Marked beads released: More marks should shrink the error, with less gain at the top.

Make it yours

Test the effect of unequal catchability, or of marks that fall off.

Safety

No hazards. This models ecological method rather than studying animals.

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