Over the past decade, the survival rate of juvenile snow leopards in the highland habitat of the Altai Mountains has steadily decreased. Similarly, the survival rate of juvenile snow leopards in the lowland habitat of the same mountain range has also steadily decreased. These two habitats account for the entirety of the snow leopard population in the region. Yet, contrary to expectations, wildlife biologists report that the overall survival rate of juvenile snow leopards across the entire Altai region has actually increased over this ten-year period.
Which one of the following, if true, most helps to resolve the apparent discrepancy described above?
- AOver the past decade, the absolute number of juvenile snow leopards born in the Altai region has increased at a rate that far outpaces the corresponding decline in the survival rates of either habitat.
- BTen years ago, the survival rate of juvenile snow leopards in the highland habitat was only marginally higher than the survival rate in the lowland habitat, although both rates were significantly higher than average.
- CThe proportion of the total snow leopard population that consists of vulnerable juveniles, rather than fully mature adults, is significantly lower today than it was a decade ago.
- DRecent conservation efforts have effectively eliminated the primary predator of snow leopard cubs in the lowland habitat, though this predator was never present in the highland habitat.
- The highland habitat has always maintained a substantially higher juvenile survival rate than the lowland habitat, and over the past ten years, the vast majority of the region's snow leopard births have shifted from the lowland to the highland habitat.Cevap
Cevap
The statement explaining that the highland habitat has always had a much higher survival rate and that the vast majority of births have recently shifted to this habitat is the correct answer.
This option resolves the paradox by employing a statistical phenomenon known as Simpson's Paradox. The overall survival rate is a weighted average of the highland and lowland rates. Even if the individual rates in both habitats decrease, the overall average can increase if a large enough proportion of the population moves from the low-survival habitat to the high-survival habitat. Because the highland habitat's survival rate is substantially higher, shifting the vast majority of births to this habitat pulls the overall regional average drastically upward, easily overpowering the individual declines within each separate habitat.
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Simpson's Paradox and Shifting Denominators
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