A claim that one action caused an outcome calls for checking the study design, or how the groups were formed. Comparing existing groups can show that an action and an outcome are associated, but it cannot by itself isolate a cause. Look for random assignment before accepting a causal claim; observing groups at the same time does not eliminate other differences between them.
Hints
- Hint 1
A comparison group gives you a baseline. Comparing a group that received a campaign with one that did not can reveal a difference in flu incidence. Does that difference tell you what caused it?
- Hint 2
In random assignment, chance decides who receives a treatment. Here, the researcher compared two cities that already differed in campaign exposure. What other differences between the cities could affect flu incidence?
Step-by-step
Check how the groups were formed
Step 1Identify what the comparison shows
No Desmos needed. The question asks whether the study can show cause, not for a calculation. City B, with no campaign, is a comparison group: its flu incidence gives the researcher a baseline for City A's. City A's lower flu incidence shows a difference between the cities, but it does not yet explain that difference.
- Step 2
Check whether the campaign was isolated
In random assignment, chance decides who receives a treatment. No random assignment is described here: the researcher compared two cities, which might also differ in residents' ages or access to vaccination. Either difference could affect flu cases. A comparison group shows a difference; random assignment helps isolate its cause.
- Step 3
Judge the causal conclusion
The result shows an association, meaning campaign exposure and lower flu incidence occurred together in this comparison. Because another city difference could explain the result, the study does not establish that the campaign caused the reduction. The best evaluation points to the missing random assignment. Choice C.