Researchers studied four reforestation projects and reported tree survival (% after 3 years) along with two factors: planting density (high/low) and presence of irrigation (yes/no). Project A, high density + irrigation, 78%; B, high density + no irrigation, 35%; C, low density + irrigation, 82%; D, low density + no irrigation, 65%. The researchers concluded that irrigation had a much larger effect on survival than planting density did. The strongest data support is ______
Which choice most logically completes the text using the data above?
- A
the average survival across projects.
- B
Project C's highest survival of 82%.
- C
Project B's lowest survival of 35%.
- Dcheck_circle
irrigation's within-density effects (A vs. B: +43 points; C vs. D: +17 points) versus density's within-irrigation effects (A vs. C: -4 points; B vs. D: -30 points)—irrigation adds 43 in one comparison while density's effect runs from -4 to -30.
Explanation
To argue irrigation has a much larger effect than density, examine each variable's effect while holding the other constant. Choice B does this for both variables and shows irrigation's effects (+43, +17) include a larger maximum than density's (-4, -30 are smaller in magnitude). This is the only choice that quantitatively addresses the comparison.