PrepTest 150, Section 3, Question 7
Pollster: When opinion researchers need a population sample(69 more words not shown)
Which one of the following(9 more words not shown)
- AUsing data from(25 more words not shown)
- BAmong people who(19 more words not shown)
- CThe group of(28 more words not shown)
- DThe people who(29 more words not shown)
- EThe percentage of(21 more words not shown)
Reading the argument
Fewer responses don't automatically mean a less accurate picture.
The census is doing a particular job here: it tells researchers what the population looks like demographically, so they can choose a sample with a similar mix. It isn't itself a poll of everyone's opinion on the issue being studied.
Even the mandatory census misses people. My first question would be how many and who. Missing five people out of a hypothetical population of 300 million is different from missing five percent. And if one group is especially unlikely to respond, a sample based on that information could underrepresent that group. A large data set isn't automatically a representative one.
Now make participation voluntary. We're told fewer people would participate, but would that make the demographic picture worse? Perhaps the smaller group would preserve the same mix. Perhaps the current picture is already skewed and the change would leave that skew unchanged—or even reduce it. Those are possibilities, not claims about what would actually happen.
What we’re looking for
For the required assumption, I'd initially look for the connection between lower participation and worse polling results. The argument needs the participation change to damage the information used to choose the sample; merely making the respondent list shorter doesn't explain that damage.
Working the answers
- A
There could be another sampling method while these researchers still rely on census data. Having an alternative doesn't mean they use it, and the argument doesn't need an alternative to exist in the first place. A doesn't supply the missing link between a voluntary census and less accurate results from the described method.
- B
Some current nonparticipants could join a voluntary census while a larger number of current participants leave. The overall participation rate could still fall, as the premise says. The argument doesn't need to rule out those new participants; it needs to establish how the changed participation affects the demographic information.
- CCorrect
This gives a minimum condition for the proposed change in the demographic picture: the voluntary participants must differ demographically from the mandatory participants. If the groups had the same characteristics in the same proportions, the census would give researchers the same demographic guide for selecting their samples, just from fewer responses.
Be precise about what C supplies. 'Different' doesn't necessarily mean less representative. The new mix could be better, worse, or differently distorted. C doesn't prove the whole conclusion; it gives a change the argument needs before it can claim that the demographic basis of polling becomes worse.
- D
Refusing an opinion poll is different from failing to participate in the census. The argument concerns how census information guides sample selection, not whether the two kinds of nonparticipants have matching demographics. The groups could differ while a voluntary census still damaged that guide.
- E
Participation under the current mandatory system could fluctuate between censuses. That doesn't prevent a switch to voluntary participation from changing the results. E concerns stability across past or successive mandatory censuses, not the effect of the proposed change in the requirement.
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