The introduction of speed cameras on British roads has been followed by a reduction in road traffic accidents. In areas where cameras were installed in 2018, accident rates fell by an average of 23% over the following two years. This demonstrates that speed cameras are highly effective at preventing accidents. Critics argue that cameras are simply revenue-generating devices, but the evidence clearly shows they save lives. Some have suggested that accident rates were already falling before cameras were introduced, but this misses the point: accidents fell further after camera installation. The government should respond to this success by installing cameras on all major roads, which would prevent thousands of accidents annually. Which one of the following best identifies the flaw in the above argument?