Question

Suppose you read a research report that claimed to have uncovered a finding with significant implications for policy. The researchers summarize the results of a multicity homicide reduction program that they claim was markedly effective. They support this claim by pointing out that, during the study period, there was a mean reduction of 1,80 homicides per month across the cities in the sample. Along with that mean, they report a 95% confidence interval of -0,40< u<4 (i.e., 1,80+ 2,20). What is wrong with the researchers claim that this program was effective? Identify the flaw in their logic and explain why that flaw makes their claim unsupportable.

Answer 1

95% confidence interval of true mean reduction of homicides per month is -0.40 < u < 4

The lower limit of the confidence interval is negative and thus, confidence interval contains negative values. We are not 95% confident that the true mean reduction of homicides per month is positive and thus, the researchers claim that this program was effective in reducing the homicides is not valid. Since the  confidence interval contains negative values, the claim is unsupportable.