The Effect of Sample Size on the Accuracy of Estimating Population Size
Lincoln index is a means of estimating population. It is also called the Capture - Mark –
Release – Recapture method. Population is calculated using the following equation:
Total Population =
Or:
N=
(n1 X n2) / m2
Number caught x Number re-caught
Number marked in the re-catch
Where N = Population Estimate
n1 = Number caught initially
n2 = Number re-caught
m2 = Number marked in the re-catch.
Research Question:
What effect does Sample size have on the accuracy of estimating population size using
the Lincoln Index?
Hypothesis:
Procedure:
1. Obtain a bag with an unknown quantity of beans.
2. Obtain a bag with a number of differently colored. (you will use these to replace
your sampled population with a “marked” population
3. Without looking, remove 10 beans from your original population and “mark”
them (ie replace them with a differently colored bean)
4. Mix up the beans.
5. With your eyes shut pick out 10 beans. Record the amount of re-catch (n2).
6. Record the number of marked beans (m2)
7. Calculate the Lincoln Index
8. Repeat stages 4 through 7 five more times. Calculate the average Lincoln Index.
9. Capture and release 10 more beans. (so now your original sample size is 20)
10. Repeat stages 4 to 8.
11. Repeat with an original sample size of 30, 40, 50 and 60 individuals.
12. Count your original bean population.
13. Combine your data with that of the class. (Every other group started with a
different population size)
Data collection and processing - Record your data in a logical way. Describe the
calculations you do to work out population estimation and how did you gauge accuracy?
Present your data in graphical form. (Select the most appropriate form!)
Discuss - What did you find ou? How does the Lincoln index work? What factors might
affect how big a sample you can get? What can affect the accuracy of the Lincoln index
in the real investigation of ecosystems? Did these factors affect your experiment?
Evaluate - Were there any errors in your experiment? How could your experiment be
improved? How realistic was your experiment to real world studies?
Conclude – What happened to accuracy of population estimation as sample size
increased? What did you expect to happen? Why? Did your results support your
hypothesis? If not, why not?