The hypothesis is that "the performance gains were caused by the workers' increased perception of their work as mentally engaging and important."
To evaluate this hypothesis, we need to know if the cause (increased perception) is truly linked to the effect (performance gains), and if there are any alternative explanations.
Let's look at the options:
(A) Whether clerical workers who perceive their jobs as important are more likely to remain in their positions long term
This relates to job retention and satisfaction, not directly to current performance gains (typing speed, error reduction) or the hypothesized cause. It doesn't help confirm or deny that the perception led to the performance.
(B) Whether those in the first group changed their time spent on personal distractions after receiving the message
This is highly relevant! If the first group spent less time on personal distractions (e.g., checking social media, chatting) because they perceived their work as more engaging, that could be the direct cause of their increased typing speed and error reduction. This would provide a mechanism for how the "increased perception of their work as mentally engaging and important" translated into performance gains. If they spent less time on distractions, it supports the idea that their changed perception led to a change in behavior, which then led to the performance. If they didn't, it might weaken the link or suggest another mechanism. This helps evaluate how the perception influenced performance.
(C) Whether both groups were equally likely to have prior experience in clerical tasks
The problem states that workers were "randomly assigned to two equal groups." Random assignment is designed to minimize pre-existing differences between groups, including prior experience. While confirming it would be good for experimental rigor, the random assignment already suggests this difference should be minimal and likely not the cause of the change observed after the message. This primarily relates to the validity of the experiment's design, not directly the hypothesis about why the change occurred.
(D) Whether the workers in the first group reported greater satisfaction with their pay after receiving the message
Pay satisfaction is a different factor from perception of work engagement and importance. While it might influence overall morale, the hypothesis specifically links perception of work to performance gains. Pay satisfaction could be an effect of higher morale, but it's not the cause proposed by the researchers.
(E) Whether routine clerical tasks are commonly perceived as cognitively undemanding
This provides background information about the general perception of these tasks. It helps explain why the message was significant ("cognitively demanding and vital"). However, knowing the common perception doesn't help evaluate whether in this specific experiment, the change in perception (from the message) actually caused the performance gains. The experiment already establishes that one group was told their tasks were important, implying a shift in perception for that group.
Conclusion:
Option (B) is most useful because it probes the mechanism by which the hypothesized cause (increased perception of engagement/importance) could have led to the observed effect (performance gains). If the workers became less distracted because they found the work more engaging, it directly supports the researchers' hypothesis. If their distraction levels didn't change, it suggests the performance gains might have resulted from another factor related to the message, or the hypothesis might be incomplete.
The final answer is B