Logical reasoning PrepTest 150 · Section 3 · Question 7

Incorrect. If anything, having alternative means of forming a representative sample weakens the argument by suggesting pollsters could switch to those methods if the census becomes skewed.

Incorrect. This answer choice states that the group skipping the mandatory census would overlap, maybe completely, with the group skipping the voluntary one. That draws those samples together, which is the opposite of what we're looking for.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Necessary Premise

Stimulus Summary:
National opinion polls base their samples on the census. The census is mandatory, but not everyone participates. If the census were voluntary, fewer people would respond, and these polls would be more inaccurate.

Answer Anticipation:
The argument concludes that changes to the way the census is conducted would make opinion polls less likely. What connects the census and opinion polls? The people included. The proposed change to the census takes it from mandatory to optional. For that to impact accuracy, the group that responds to an optional census must be different from the one that responds to a mandatory one, and it has to be less representative of the public as a whole.

Answer Explanation:
This answer choice directly states that the two response groups would be different. For there to be a change in accuracy, the groups responding must be different, so this answer is correct. Note that this isn't also a Sufficient Assumption—it leaves open the possibility that the voluntary group is more representative of the population as a whole.

Key Takeaway:
When a conclusion makes a comparison, the correct answer will likely provide information that can be used to analyze if the two things being compared are similar or different, so prioritize answers that allow you to do that.

Incorrect. While this answer suggests that the current census-based opinion polling is flawed, it doesn't impact the part of the argument that compares it to a hypothetical situation where the census is done on a voluntary basis. Since the conclusion is comparative, an answer that doesn't play into that comparison is unlikely to address the assumption.

Incorrect. The demographic information of the census in-group is important, not the size of it.