QUESTION 35 (5 marks)
Forty possums are captured, marked and released. A second capture contains 50 possums, of which 10 are marked.
a) Use the Lincoln index to estimate the population. [2 marks]
b) Explain how loss of marks before the second capture would affect the estimate, with other factors unchanged. [2 marks]
c) State one other assumption of this estimate. [1 marks]
Practice marking scheme
Answer
a) 200 possums. b) An overestimate. c) For example, a closed population or equal capture probability.
Working
. Loss of marks causes some previously marked animals to be recorded as unmarked, reducing the observed . Since is the denominator, the estimate increases. Other assumptions include negligible births, deaths, immigration and emigration between captures, sufficient mixing and no effect of marking on capture probability.
Marking criteria
- Substitutes 40, 50 and 10 correctly. [1 mark]
- Calculates 200. [1 mark]
- Explains that loss of marks lowers the observed marked recaptures. [1 mark]
- Predicts an overestimate and links this to the denominator. [1 mark]
- States one appropriate additional assumption. [1 mark]
Practice question aligned to the current QCAA syllabus; review the worked solution and marking criteria.
View the QCAA syllabusCompare your working with the guide above.