This dataset contains the labor force participation rate (LFPR) of women in 19 cities in the United States in each of two years (1968 and 1972). The data help to measure the growing presence of women in the labor force over this period.
It may seem reasonable to compare LFPR rates in the two years with a pooled t-test since the United States did not change much from 1968 to 1972. However, the data are natually paired because the measurements were made in the same cities for each of the two years. It is better to compare each city in 1972 to its own value in 1968.
The data offer a good example of how a paired t-test can be more effective when it is appropriate. Here, a pooled t-test is not significant, but a paired test is significant and the .05 level for testing the null hypothesis of no change in the LFPR between 1968 and 1972.