A table question with a cutoff tests whether you can draw a conclusion under the text’s rules. Read the sentences explaining what the numbers measure and which changes count. Then read the title and column headings so you can compare each treatment with its own standard value. A change counts only if its size reaches the stated cutoff. Check what the measurement can show, because a choice can get the numbers right and still go past the text.
Hints
- Hint 1
Look at what a higher ratio tells you in the sentence explaining the measurement. What does the passage say you can and can’t learn from that ratio?
- Hint 2
Compare each treatment with the same species under standard conditions. With two treatments for each of two grasses, work out four differences.
- Hint 3
How does each difference compare with the researchers’ 0.10 cutoff for a reliable response?
Step-by-step
Compare each treatment with its species’ standard mean
Step 1Identify what the ratio shows
The passage says a higher ratio means greater root biomass relative to shoot biomass, which limits what we can conclude. Can it tell us that root biomass itself increased? No, because it does not indicate whether absolute root biomass has increased. The ratio compares root biomass with shoot biomass, rather than measuring a gain in roots alone.
- Step 2
Set the comparison and cutoff
Which changes count as reliable? The researchers set the cutoff at a difference of at least 0.10 from the mean for the same species under standard conditions. The title gives ratios, and the headings separate standard conditions, low nitrogen, and low water. The researchers compare each treatment with the same grass under standard conditions, so we compare treatment and standard values within the same row.
- Step 3
Calculate all four changes
For prairie dropseed, low nitrogen gives 1.29 − 0.84 = 0.45, and low water gives 0.88 − 0.84 = 0.04. What happens when we use sideoats grama’s standard ratio of 0.79? Low nitrogen gives 0.83 − 0.79 = 0.04, while low water gives 1.24 − 0.79 = 0.45. The larger increase comes from a different treatment for each grass.
- Step 4
Apply the cutoff to the conclusion
Apply the at least 0.10 cutoff: the 0.45 increases are reliable, but the 0.04 increases aren’t. So low nitrogen counts as reliable for prairie dropseed alone, and low water counts as reliable for sideoats grama alone. The choice’s greater relative belowground allocation describes root biomass compared with shoot biomass, which stays within what the ratio can show. Choice D.