A causal claim says one action produced a result, not merely that two things happened together. To evaluate a comparison of group averages, first check how the groups formed and what else could differ between them. A higher average alone doesn't settle whether the plan or another difference produced the result.
Hints
- Hint 1
A causal claim says the plan produced the result, not merely that plan use and weight loss happened together. Before judging the averages, ask who decided whether each person used the plan.
- Hint 2
A confounding variable is another difference that could affect weight loss, such as exercise habits. If exercise habits differed between the groups before the study began, could those habits explain part of the gap?
Step-by-step
Check how the groups were formed
Step 1Identify who chose the groups
No Desmos needed. This question asks how the groups were formed, not for a calculation. The company compared customers who purchased the plan with people who didn't. So the people chose whether to use it. This is an observational study: the company recorded their choices rather than assigning them to groups.
- Step 2
Look for another possible cause
People who buy a meal plan might also exercise more or have different weight-loss goals. Either could be a confounding variable, another factor that affects weight loss. Because the groups were not randomly assigned, such differences might explain some or all of the gap. A comparison group shows a difference; random assignment helps establish what caused it.
- Step 3
Judge the company's claim
The averages show that plan users lost more weight on average, but not why. Since people chose their groups, the study cannot prove that the plan itself caused the difference. The explanation pointing to missing random assignment fits. Choice C.