Question

A regional transportation authority is interested in estimating the mean number of minutes working adults in the region spend commuting to work on a typical day. A random sample of working adults will be selected from each of three strata: urban, suburban, and rural. Selected individuals will be asked the number of minutes they spend commuting to work on a typical day. Why is stratification used in this situation?

Answer 1

Answer:  To remove bias when estimating the proportion of working adults living in urban, suburban, and rural areas.

Explanation: In simple words, stratification refers to the process in which different sections of the society are grouped on the basis of one or more general factors.

In the given case, the company wants to estimate the minutes of working adults in the region and the region is grouped into urban, suburban and rural.

Thus, the random selection from different regions is done so that no bias takes place regarding the number of adult working in these three different areas.

Answer 2

Correct Answer:

To decrease the variability in estimates of the mean commuting time

Explanation:

Because stratifying the population into relatively homogeneous groups of sampling units reduces sampling error, estimates generated within strata have higher precision than simple random samples drawn from the same population. Thus, variability is minimized within stratas that are similar.