A survey can have selection bias when the way people are chosen favors those likely to give a particular answer. Compare the group the researcher wants to describe with who could enter the sample. A sample tied to the survey topic cannot automatically represent the wider group. Getting more answers from the same source does not fix that problem.
Hints
- Hint 1
The target population is the full group the researcher wants to describe. Look at the researcher's goal: is it to learn about all county adults or only people who took part in the event?
- Hint 2
A sample is the group actually surveyed. Ask who had a chance to be picked at the finish line. Could a county adult who didn't enter the race have been surveyed there?
Step-by-step
Compare the target group with the surveyed group
Step 1Identify the group the researcher wants to describe
No Desmos needed. This question is about who was surveyed, not arithmetic.
The target population is the full group the researcher wants to describe. The researcher wants to estimate exercise habits for adults in the county, so any countywide claim needs evidence that represents that group.
- Step 2
Identify who could enter the sample
The sample is the group actually surveyed. At the finish line, only race finishers could be among the next people questioned. County adults who didn't enter the race had no chance to be picked.
- Step 3
Decide whether that sample represents county adults
People who finish a race may be more likely to exercise regularly than county adults overall. That's selection bias: the way respondents were chosen favors people likely to answer yes. The survey is biased because it includes only people who participate in the race. Choice B.