Deciles and Quintiles For a given data set, there are nine deciles, denoted by D1, D2, . . . , D9 which separate the sorted data into 10 groups, with about 10% of the values in each group. There are also four quintiles, which divide the sorted data into five groups, with about 20% of the values in each group. (Note the difference between quintiles and quantiles, which were described earlier in this section.)

a. Which percentile is equivalent to D1? D5? D8?

b. Using the sorted cotinine levels of smokers in Table 2-13, find the nine deciles.

c. Using the sorted cotinine levels of smokers in Table 2-13, find the four quintiles.