Individuals filing federal income tax returns prior to March 31 received an average refund of $1068. Consider the population of last-minute filers who mail their tax return during the last five days of the income tax period (typically April 10th to April 15th). A researcher suggests that a reason individuals in that population wait until the last five days is that on average these individuals receive lower refunds than do early filers. For a sample of 432 individuals who filed a tax return between April 10th and 15th, the sample mean refund was $956. It is known that population standard deviation is $619. Calculate the appropriate test statistic. Round your answer to three decimal places. Answer: