Question 141·200 Super-Hard SAT Reading Questions·Information and Ideas
Seedling Survival and Soil Moisture after a Dry Season
| Canopy setting | Leaf-litter treatment | Seedlings surviving (%) | Average soil moisture (%) |
|---|---|---|---|
| Open | Retained | 57 | 18 |
| Open | Removed | 34 | 11 |
| Shaded | Retained | 68 | 24 |
| Shaded | Removed | 62 | 22 |
Ecologists studying young forest plants hypothesized that keeping naturally fallen leaves around seedlings would improve dry-season survival by reducing soil-water loss. They further predicted that this benefit would be greater in open patches than in patches shaded by a tree canopy. In each canopy setting, the researchers randomly assigned similar plots either to retain or to have their leaf litter removed. The table shows the results after one dry season.
Which choice identifies the finding that most directly supports the researchers’ hypothesis?
For evidence questions involving a hypothesis with two conditions, translate the hypothesis into the exact comparison the data must show. Here, the key quantity is not the highest table entry or a comparison across canopy settings under only one treatment, but the treatment difference within each canopy setting. Calculate those differences, compare them, and select the option that addresses every part of the hypothesis.
Hints
Focus on the full prediction
The highest value in the table does not necessarily provide the best evidence. Determine what pattern the researchers predicted across the two canopy settings.
Isolate the litter treatment
Within each canopy setting, subtract the value for removed litter from the value for retained litter.
Compare the treatment effects
After finding the two differences for each canopy setting, identify the choice that accurately compares their sizes for both measured outcomes.
Step-by-step Explanation
Identify the required comparison
The researchers predict not only that retaining litter will help but also that its benefit will be greater in open plots. Therefore, compare retained-litter plots with removed-litter plots separately within each canopy setting.
Calculate the treatment differences in open plots
In open plots, the survival difference is percentage points, and the soil-moisture difference is percentage points.
Compare with the differences in shaded plots
In shaded plots, the corresponding differences are only percentage points for survival and percentage points for soil moisture. Both treatment advantages are larger in open plots, exactly matching the hypothesis.