Question 111·Hard·Command of Evidence
Correlations Between Photosynthesis Rate and Environmental Variables in Greenhouse Tomato Plants
| Environmental variable | Morning | Afternoon | Overall |
|---|---|---|---|
| Light intensity | 0.942 | 0.968 | 0.955 |
| Soil moisture | 0.673 | 0.712 | 0.698 |
A team investigating factors that influence photosynthesis in greenhouse‐grown tomato plants measured the plants’ photosynthetic rates along with light intensity and soil moisture in the morning and afternoon. The researchers then calculated the correlations shown in the table and concluded that photosynthesis is more strongly associated with light intensity than with soil moisture.
Which choice best describes data from the table that support the researchers’ conclusion?
For SAT data-support questions, first restate the conclusion in your own words (here: “light intensity has a stronger correlation with photosynthesis than soil moisture does”). Then, scan the table to see if the numbers consistently fit that idea—compare matching entries (morning vs morning, etc.) and note which are larger or farther from 0. Finally, choose the answer that clearly and accurately describes that pattern; be careful with options that are merely true but don’t compare the right things, or that focus on one variable or one time period instead of the full pattern the conclusion is based on.
Hints
Focus on what "more strongly associated" means
Look at the word "correlation" in the table. How does the size of a correlation (how far it is from ) relate to how strong the association is?
Compare pairs of numbers, not just single values
For each time period (morning, afternoon, overall), compare the light-intensity correlation to the soil-moisture correlation. In each pair, which number is farther from ?
Match the pattern to a choice
Once you see the pattern in the table, look for the answer that clearly describes that pattern across all time periods, not just one time period and not just one variable alone.
Step-by-step Explanation
Understand what the conclusion is claiming
The conclusion says that photosynthesis is more strongly associated with light intensity than with soil moisture.
For correlations, a value closer to or (and farther from ) means a stronger relationship. So we are looking for evidence that the correlation with light intensity is stronger (farther from ) than the correlation with soil moisture.
Read and compare the correlations in the table
Now compare the pairs of correlations for each time period:
- Morning:
- Light intensity:
- Soil moisture:
- Afternoon:
- Light intensity:
- Soil moisture:
- Overall:
- Light intensity:
- Soil moisture:
In each case, the light-intensity correlation is a larger positive number and therefore farther from than the soil-moisture correlation. This matches the idea of a stronger association with light.
Check which option actually supports that comparison
Now see how each answer choice relates to the conclusion:
- One choice talks about a specific threshold () and says only one time period exceeds it.
- One choice just says both correlations are positive.
- One choice compares overall soil moisture to morning soil moisture only.
- One choice directly describes that, for every time period, the light-intensity correlation is farther from than the soil-moisture correlation.
We want the option that clearly and accurately states that light intensity has the stronger correlation in each time period.
Identify the choice that matches the data and conclusion
The only option that directly states the needed pattern—that for each time period, the correlation with light intensity is farther from 0 than the corresponding correlation with soil moisture—is:
For each time period, the correlation with light intensity is farther from 0 than the corresponding correlation with soil moisture.