PrepTest 122

Incorrect. This answer would explain a difference between Group 1 and Groups 2 and 3 since the latter two groups used sterilized toothbrushes. Since the results showed a difference between Group 3 and Groups 1 and 2, this answer doesn't provide a resolution to the paradox.

Correct. Argument or Facts:
Facts

Question Type:
Paradox

Stimulus Summary:
Group 1 — Same toothbrush all year, never sterilized (gross)
Group 2 — Same toothbrush all year, sterilized each month (less gross)
Group 3 — New sterilized toothbrush each month (not gross)
Results — Groups 1 and 2 had the same plaque; Group 3 had less plaque

Answer Anticipation:
This Paradox question, as with many Paradox questions, is all about the comparison. It also has three groups being compared, which makes it important to note which groups are noted as being similar, and how so.

Let's start with the results—Groups 1 and 2 saw similar results, whereas Group 3 had different results. As such, we should identify what's similar between the first two groups that's different from the third.

Looking at that, the similarity between Groups 1 and 2 that's different from Group 3 is whether there was a new toothbrush. The first two groups used the same toothbrush all year, whereas the third had a new one each month. This suggests that the different outcome is related to the new toothbrush, and we should look for an answer suggesting that (maybe plaque removal is better with a fresher toothbrush).

Note that the sterilization is going to be brought up in trap answers—it's a similarity between the second and third groups, and thus it can't explain a difference between those two groups.

Answer Explanation:
This answer establishes bristle stiffness as being important in the level of plaque on the teeth. Since stiffness is higher in newer brushes, and Group 3 was the only group to use new brushes throughout the year, this answer explains why that group saw lower levels of plaque than the other two by the end of the year.

Key Takeaway:
When a Paradox question brings up groups that have similarities and differences, start by identifying the paradox—what similarity or difference are you attempting to explain? From there, you can identify which details from the stimulus are likely to be related to that paradox. Here, we were looking to explain a difference between Group 3 and Groups 1 and 2, so a difference between Group 1 and the other groups wouldn't be relevant.

Incorrect. Two issues here. First, this answer doesn't establish if this method is better or worse than the standard method. Second, it would have been used for all three groups, so even if it were more inaccurate, it should still have been able to measure relative plaque levels.

Incorrect. First, there being some" people in one group who had this feature isn't necessarily enough to throw the results off. Second, there's no indication that the same isn't true for the other groups, information which is necessary to analyze the effect this would have on the situation. Third, a year should be enough time to normalize the effects of brushing on plaque levels.

Incorrect. This answer establishes a similarity between all the groups, which won't help to explain a difference between one and the other two.