A survey that records people’s existing habits and outcomes is an observational study. First check who was randomly sampled to see whom the result can describe. Then check whether people were randomly assigned to a habit before claiming cause. Random sampling sets the population; random assignment supports causation. A difference between group averages doesn’t show what caused it.
Hints
- Hint 1
A simple random sample gives each member of the sampled population the same chance of selection. That helps the result speak for that population. Which adults could have been selected here?
- Hint 2
Selecting adults randomly isn’t the same as randomly assigning them to eat different amounts. To establish causation, you need to ask who formed the groups. Did the researcher set anyone’s diet, or only record what they reported?
- Hint 3
An association means two things go together without proving why. The result compares group averages, not each person’s cholesterol before and after a diet change. What wording describes the observed difference without promising an individual change?
Step-by-step
Check sampling, then assignment
Step 1Identify whom the sample can represent
No Desmos needed. This is about study design, not calculation. A simple random sample gives each adult in City X the same chance of selection, so the findings can reasonably describe adults in City X.
- Step 2
Check how the eating groups formed
The researcher recorded what adults reported eating; no one was randomly assigned a diet. This is an observational study: the adults’ existing habits formed the groups. Other differences between the groups, such as exercise, could also affect cholesterol, so the survey cannot show that servings caused the difference.
- Step 3
Describe the difference without claiming cause
The adults reporting at least servings had cholesterol levels milligrams per deciliter lower on average than the other group. That’s an association, a pattern between two measured traits, not a promise of a drop for any person. So eating at least servings is associated with lower cholesterol among adults in City X. Choice B.