For evidence-validity questions, compare the exact scope of the evidence with the exact scope of the claim. Pay special attention to conditional statistics such as averages calculated only among people who acted; if the conclusion applies to everyone, look for missing information about those excluded from the calculation.
Hints
- Hint 1
Check the populations
Compare the group included in the reported mean with the broader group covered by the researchers' conclusion.
- Hint 2
Consider zero contributions
Ask what additional information is needed to account for purchasers who encountered a contribution field but gave nothing.
Step-by-step
- Step 1
Compare the evidence with the claim
The evidence reports the mean gift among donors, whereas the claim concerns revenue per ticket purchaser, including purchasers who donated nothing.
- Step 2
Identify the missing information
A larger mean gift among donors does not guarantee greater revenue per purchaser. If the prefilled field caused sufficiently fewer purchasers to donate, its higher mean gift could be offset by its lower donation rate.
- Step 3
Select the decisive question
The percentage of purchasers who donated in each condition would allow the researchers to account for zero contributions and compare donation revenue across all purchasers.