Identify a pair of variables for which you would expect to see a strong correlation but not a cause-and-effect relationship. Suggest an explanation for the association.
Twenty years ago, postal employees worked for the postal service an average of 7.5 years. Recently, a sample of 100 postal employees revealed that the average time these employees had worked for the postal service was (x') = 7 years. The population of employee lengths of service has a standard deviation = 5 years. Has x' decreased from the mean of 7.5 years of 20 years ago? Conduct a hypothesis test (use H0: µ =7.5). Use a .05 significance level. Is this evidence that the average length of employment with the postal service has decreased from twenty years ago?