Another Test Question: Analyzing an Argument
Here is another practice GRE question on Analytical Writing, and my answer follows. How do you think I did?
Six months ago the region of Forestville increased the speed limit for vehicles traveling on the region's highways by ten miles per hour. Since that change took effect, the number of automobile accidents in that region has increased by 15 percent. But the speed limit in Elmsford, a region neighboring Forestville, remained unchanged, and automobile accidents declined slightly during the same six-month period. Therefore, if the citizens of Forestville want to reduce the number of automobile accidents on the region's highways, they should campaign to reduce Forestville's speed limit to what it was before the increase.
Although prima facie, this looks like a reasonable argument, the evidence given in this argument is insufficient to warrant the conclusion. There are too many unknown factors that may be relevant to weakening the argument. The argument must assume there are not possible alternative plausible explanations of the data that may lead to identifying a different cause for the increase in automobile accidents. For example, the evidence does not contain information about whether or not the accidents are taking place in parking lots and backroads or on the actual highways where the speed limit was changed. What if the 6-month period is during the winter and all the increase in accidents could be traced to a few hot spot areas on steep backroads in Forestville, and Elmsford does not have comparable steep backroads? What if the amount of accidents increases by 15 percent during the winter in Forestville every year, not just the year in which the speed limit was increased by 10 miles on the highways? What if the speed limit in Forestville was changed because of an increase in traffic, which increase in traffic might also account for the increase in accidents for the same reasons that crime activity goes up in proportion to the increase in human population? The argument could be strengthened by ruling out these possible alternatives through demonstrating that this 6-month increase in accidents does not occur every year, and that the backroads and parking lots have not been the key areas where the accidents have occurred.