PrepTest 142, Section 1, Question 18

What we’re looking for

Working the answers

• A
  Correct

  This offers a different causal objection. Perhaps a third factor influences both how much people sleep and how often they become ill. Diet, for example, is something we might investigate as a possible influence on both. We haven't established that it has those effects; it illustrates the kind of explanation the researcher overlooks.

  If another factor helps produce both parts of the pattern, less sleep needn't be strengthening anyone's defenses. A exposes the same central problem as our initial objection: the observed relationship doesn't establish the researcher's proposed cause. It does so through a shared cause rather than the reverse direction we predicted.

• B

  The argument doesn't claim sleep is the only factor affecting illness. Even if sleep had the protective effect claimed, other factors could matter too. The problem is establishing that effect at all. Pointing out that an effect can have multiple causes doesn't identify the unsupported inference from this survey.

• C

  This would require a rule saying a particular condition guarantees an outcome, followed by the outcome and a conclusion that the condition occurred. We aren't given that sort of rule. We have an observed statistical relationship and a causal interpretation of it.

• D

  This runs in the wrong direction. The researcher does not begin with a known causal connection and assume a visible correlation will follow. The correlation is what the survey supplies. The researcher then uses it to infer a protective causal effect.

• E

  Other harms from sleep deprivation would be worth considering when assessing the broad claim that it isn't unhealthy. But this choice describes an absence of association with a particular negative consequence; the study actually reports different frequencies of illness, not no association. It also leaves the central claim about bolstering defenses unexplained. A directly identifies why the evidence fails to establish that supposed benefit, which is the fundamental error in the argument.