PrepTest 139

Incorrect. Exercise isn't connected to arthritis, so this answer is out of scope.

Incorrect. The stimulus controls for the amount of each type of coffee consumed by looking at only people who drink 3 cups per day.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Argument Evaluation

Stimulus Summary:
Study - Look at people who drink 3 cups/day of decaf coffee, and people who drink 3 cups/day of regular coffee
Results - The former group were twice as likely to develop arthritis
Conclusion - Something in decaf coffee causes arthritis

Answer Anticipation:
This argument starts with a study, so we should start by considering whether there's a sampling flaw or a correlation/causation flaw

As to a sampling flaw, it looked at people who drink 3 cups of both caffeinated and decaf coffee per day, and it does draw a conclusion about the population as a whole. So there might be an answer that specifically calls out a difference between three cups and other amounts of coffee, but that seems rather specific and weird—it's more likely that the 3 was picked to compare apples-to-apples as far as the amount of coffee is concerned. In order for an answer to address this sampling issue, it would have to ask about a difference between people who drink 3 cups/day and those who drink different amounts, not just that there are people who drink different amounts.

For the correlation/causation flaw, we have a causal conclusion, and studies essentially always establish correlations. That's no different here, where the consumption of decaf coffee was correlated with a higher rate of arthritis than in the other group. So there is a correlation/causation flaw here, and any answer that addresses it could be correct.

There's another feature here that's a bit related to both of these flaws that might allow us to make a more specific anticipation, and that's that the rate of arthritis is compared just between coffee drinkers. The rate of arthritis is compared between the groups of coffee drinkers, not the general population. As such, it's possible that the decaf drinkers had a normal arthritis rate—and it was actually the caffeinated coffee drinkers who had a lower rate of arthritis. This hints at a sampling flaw (there was no comparison to the "average" person), a correlation/causation flaw (alternative cause), as well as a bad comparison. Any answer that asks at the benefits of caffeine as far as arthritis is concerned would serve as a correct answer.

Answer Explanation:
This answer would help to evaluate if the correlation in question results in the causal conclusion drawn. It's possible that decaf coffee hurts connective tissue, but it's also possible that caffeine helps connective tissue. If the latter is the case, then there's an alternative cause/explanation of the results of the study. Knowing whether this alternative cause is true would help evaluate the argument, so this is the answer.

Key Takeaway:
Studies need to set a baseline against which to compare different rates. If there's no baseline set, then there's no indication if different rates represent one thing being higher than average, one thing being lower than average, or both things being off from the average.

Incorrect. Similar to (B), the stimulus controls for the amount of each type of coffee consumed by looking only at a certain group. That said, the argument also concludes that decaf has something caffeinated coffee doesn't that causes arthritis, so the amount of caffeinated coffee consumed wouldn't have much to do with that.

Incorrect. If the argument concluded that decaf coffee was the only or primary cause of arthritis, then this answer would help evaluate it. However, it just raises it as one causal factor in arthritis, so highlighting that a lot of arthritis sufferers don't drink any type of coffee and thus something else led to their arthritis wouldn't help evaluating the connection in the stimulus.