In response to office workers' worries about the health risks

Conclusion: VDTs cause headaches.
Evidence: Frequent VDT users suffered from headaches more often than other office workers did.
Relevant factor influencing evidence: the time spent using VDTs is based on an ESTIMATION. So is the frequency of the occurrence of headaches.

Option A. Who are the FEW office workers in question? Are they those who suffered headaches, or those who did not? It would be helpful to know this. Furthermore, does the participation in a health program - regular or otherwise - ensure that one will not have headaches - and even if it did, what would be the connection between that and the effects of using VDTs regularly? IRRELEVANT.

Option B. The distinction between mild and severe headaches narrows the scope of the passage and so makes this option irrelevant. The passage is talking about headaches in general, and this general category encompasses all possible degrees of severity. IRRELEVANT.

Option C. The passage draws a conclusion on the basis of a particular survey: therefore, the weakening or strengthening of that conclusion must occur within the framework of factors relevant to the survey. What previous studies have shown is therefore beside the point. Furthermore, the conclusion that we are asked to weaken involves headaches: eyestrain has nothing to do with it. IRRELEVANT.

Option D. We need to take note of the fact the evidence used in the researchers' survey is vitiated (as is the conclusion) by the fact that it is based on ESTIMATIONS. These do not readily provide solid fact: they can very easily be highly subjective and wildly inaccurate. If, as this option states, the workers who experienced frequent headaches were more likely than other workers to overestimate how much time they spent using VDTs, the conclusion that VDTs cause headaches is greatly weakened. The reason for this is that if the time spent in front of VDTs by headache-sufferers is significantly less than it is estimated to be, there is significantly less evidence that VDTs cause headaches. CORRECT.

Note also that this is the only option that refers - in the word OVERESTIMATE - to the factor that vitiates the evidence and the conclusion of the argument, and is therefore a prime contender for the position of correct answer. If you were in real doubt between a number of options, this factor could help you to make an intelligent guess.

Option E. If the evidence and conclusion of the argument involved the claim that VDTs have an impact on health in general, it would be possible to state (assuming that JOB-RELATED STRESS falls under the category of HEALTH) that this option weakens the argument. The option would indicate that since this kind of stress occurs just as frequently among VDT users as among those who do not use them, VDTs are not its cause. Nevertheless, the conclusion of the passage is that VDTs cause headaches, and the evidence on which this conclusion rests is that frequent VDT users suffered headaches more frequently. We therefore have to stick with headaches. MISLEADING AND IRRELEVANT.

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