A marketing research company is estimating the average total compensation of CEOs in the service industry. Data were randomly collected from 18 CEOs and the 95% confidence interval for the mean was calculated to be
What additional assumption is necessary for this confidence interval to be valid?
◦ None. The Central Limit Theorem applies.
◦ The population of total compensations of CEOs in the service industry is approximately normally distributed.
◦ The sample standard deviation is less than the degrees of freedom.
◦ The distribution of the sample means is approximately normal.