Multivariable comparison of rates; interaction; observational limits
conservation
Rangers monitored radio-tagged kiwi chicks for six months in areas with and without intensive stoat trapping, in two habitats. The trapped areas were chosen by the regional council.
| Habitat | Trapping | Chicks | Survived |
|---|---|---|---|
| Forest | Yes | 60 | 42 |
| Forest | No | 60 | 18 |
| Scrub | Yes | 50 | 30 |
| Scrub | No | 50 | 20 |
Figure 1 shows the number of chicks that survived and died in each habitat and trapping group.
Stacked bar chart of the number of radio-tagged kiwi chicks that survived and died over six months in four groups: forest with and without stoat trapping (60 chicks each) and scrub with and without trapping (50 chicks each).Facts you may need
(a)
Calculate the survival rate in each of the four groups.
(b)
Compare the effect of trapping in the two habitats, using differences and relative risks.
(c)
A summary report combines habitats: survival 72/110 with trapping vs 38/110 without. Calculate these and explain what the combined figure hides.
(d)
Explain why these results do not show that trapping causes higher survival, and suggest a better design.
Kiwi chick survival and predator control — Scholarship Statistics | Xametric
