The following appeared in the editorial section of a newspaper in the country of West Cambria.
The practice of officially changing speed limits on the highwayswhether by increasing or decreasing themis a dangerous one. Consider what happened over the past decade whenever neighboring East Cambria changed its speed limits: an average of 3 percent more automobile accidents occurred during the week following the change than had occurred during the week preceding iteven when the speed limit was lowered. This statistic shows that the change in speed limit adversely affected the alertness of drivers.
Discuss how well reasoned... etc.
This editorial asserts that West Cambria should not change its highway speed limits because such changes adversely affect driver alertness and are therefore dangerous. To support this claim, the editorial cites statistics indicating that whenever East Cambria changed its speed limits, an average of 3 percent more automobile accidents occurred during the week after the change than during the week preceding it, even when the speed limit was lowered. As it stands, this argument suffers from three critical flaws.
First, it is unlikely that the brief one-week periods under comparison are representative of longer time periods. A difference of only 3 percent during one particular week can easily be accounted for by other factors, such as heavy holiday traffic or bad weather, or by problems with reporting or sampling. Had the editorial indicated that several speed-limit changes in East Cambria contributed to the statistic, the argument would be more convincing; but for all we know, the statistic is based on only one such change. In any event, a one-week period is too brief to be representative because it is likely that accidents will occur more frequently immediately following the change, while people adjust to the new limit, than over the longer term when drivers have become accustomed to the change.
