In estimating the total value of supplies on repair trucks, Baker Company draws random samples from two equal-sized strata of trucks. The mean value of the inventory stored on the larger trucks (stratum 1) was computed at $1,500, with a standard deviation of $250. On the smaller trucks (stratum 2), the mean value of inventory was computed as $500, with a standard deviation of $45. If Baker had drawn an unstratified sample from the entire population of trucks, the expected mean value of inventory per truck would be $1,000, and the expected standard deviation would be
Greater than $250.
The standard deviation is a measure of variability within a population. That the population was stratified indicates that each stratum has a smaller standard deviation than the population as a whole. If the two diverse populations are combined, the resulting standard deviation is likely to be larger than that of either of the separate strata. Because the standard deviations of the two strata were $250 and $45, the expected standard deviation is likely to be greater than $250.