Icecream87 wrote:
Advertisement: Most power hedge trimmers on the market do an adequate job of trimming hedges, but many power hedge trimmers are dangerous to operate and can cause serious injury when used by untrained operators. Bolter Industries’ hedge trimmer has been tested by National Laboratories, the most trusted name in safety testing. So you know, if you buy a Bolter’s, you are buying a power hedge trimmer whose safety is assured.
The answer to which one of the following questions would be most useful in evaluating the truth of the conclusion drawn in the advertisement?
(A) Has National Laboratories performed safety tests on other machines made by Bolter Industries?
(B) How important to the average buyer of a power hedge trimmer is safety of operation?
(C) What were the results of National Laboratories’ tests of Bolter Industries’ hedge trimmer?
(D) Are there safer ways of trimming a hedge than using a power hedge trimmer?
(E) Does any other power hedge trimmer on the market do a better job of trimming hedges than does Bolter Industries’ hedge trimmer?
Source: LSAT
OFFICIAL EXPLANATION
As with all questions, you must identify the conclusion of the argument. The conclusion states that if you buy a Bolter’s power hedge trimmer, you know the trimmer is safe. In the question stem, we are asked to evaluate the truth of this conclusion. Each answer choice is then posed in the form of a question. The answer choice that is correct will contain the question that, when answered, will reveal whether the conclusion is strong or weak.
In order to understand the application of the Variance Test, we will look at each answer choice in succession and thus we will not perform an initial analysis of the argument (on the LSAT we would analyze the stimulus closely). Also note that on the test we would not apply the Variance Test to each answer choice, only to the Contenders. For teaching purposes, we will apply the Variance Test to each answer in an effort to give you the best possible understanding of how the technique works.
Answer choice (A) asks if National Laboratories has performed tests on other machines from Bolter Industries. To apply the Variance Test, we should supply different and opposing answers to the question posed by the answer choice. First, try the answer “No.” With this answer, would the fact that National Laboratories did not perform safety test on other Bolters machines affect the safety of the Bolter’s hedge trimmer? No—this does not help us evaluate the safety of the hedge trimmer. What if the answer was “Yes” ? Would the fact that National Laboratories performed safety tests on other Bolters machines affect the safety of the Bolter’s hedge trimmer? Not at all. So, regardless of how we respond to the question posed in answer choice (A), our view of the conclusion is the same—we do not know whether the claim that the hedge trimmer is safe is good or bad. According to the Variance Test, if the answer is correct, then supplying opposite answers should yield different views of the conclusion. Since our assessment of the conclusion did not change, the Variance Test tells us that this answer is incorrect.
The question in answer choice (B) is, “How important to the average buyer of a power hedge is safety of operation?” Again, apply the Variance Test and supply opposite answers to the question in the answer choice. In this case, try “Very Important” and “Not Important.” If safety of operation is very important to a buyer of hedge trimmers, would that affect whether the Bolter’s hedge trimmer itself is safe? No. Let’s look at the opposite side: if safety of operation is not important at all to a buyer of hedge trimmers, would that affect whether the Bolter’s hedge trimmer itself is safe? No. Because our view of the validity of the conclusion does not change when we consider different responses to the question posed in answer choice (B), the Variance Test tells us that answer choice (B) is incorrect.
The question in answer choice (C) is, what were the results of the tests of Bolter’s hedge trimmer? Using the Variance Test, supply one response that says, “Bolter’s hedge trimmer failed the safety test.” If this is true, then the conclusion is unquestionably weakened. Now supply a response that says, “Bolter’s hedge trimmer passed the safety test.” If this is true, then the conclusion is strengthened. So, depending on the answer supplied to the question posed in answer choice (C), our view of the validity of the argument changes: sometimes we view the conclusion as stronger and other times as weaker. Therefore, according to the Variance Test, this is the correct answer. In this instance, the Variance Test reveals the flaw in the argument: the author simply assumed that being tested means safety is assured. Nowhere in the argument did the author mention that the hedge trimmer passed the tests, and the Variance Test reveals this flaw.In answer choice (D), “Yes” and “No” responses do not change our view of the argument, and answer choice (D) is incorrect.
In answer choice (E), “Yes” and “No” responses do not change our view of the argument, and answer choice (E) is incorrect.
The key thing to note is that the Variance Test is applied according to the nature of each answer choice. Thus, with some answer choices we might supply responses of “Yes” and “No,” and other answer choices might require responses of “0%” and “100%,” or “Very Important” and “Not Important.” But, in each case, the answers we supply are opposites, and the correct answer is always the one that changes your view of the validity of the conclusion when those different responses are supplied. If your view of the argument does not change, then the answer choice is incorrect.
Keep in mind that the Variance Test should only be applied to the contending answer choices. In the discussion above we applied it to every answer choice, but we did this simply to show how to effectively apply the Variance Test. During the actual test you would only want to apply the Variance Test to two or three answer choices at most.
_________________