QUESTION 33 (5 marks)
Researchers randomly locate eight 0.50 m² quadrats in a uniform 240 m² meadow. They count 3, 7, 4, 6, 5, 4, 8 and 3 orchid plants.
a) Estimate the number of orchid plants in the meadow. Show working. [3 marks]
b) Identify one sampling choice that helps minimise bias and explain its benefit. [2 marks]
Practice marking scheme
Answer
a) 2400 orchid plants. b) Random quadrat positions reduce preferential sampling of dense or sparse patches.
Working
The eight quadrats contain 40 plants in a total sampled area of . Mean density is . Estimated abundance is plants. Random positions reduce the influence of the researcher’s expectations on where plants are counted.
Marking criteria
- Totals the counts as 40 or calculates mean count 5. [1 mark]
- Calculates density as 10 plants per square metre. [1 mark]
- Estimates 2400 plants. [1 mark]
- Identifies random placement. [1 mark]
- Explains that random placement reduces location-selection bias. [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.