Page:Online Statistics Education.pdf/80

 Figure 4. Stem and leaf display with negative numbers and rounding.

Observe that the figure contains a row headed by “0” and another headed by “-0.” The stem of 0 is for numbers between 0 and 9, whereas the stem of -0 is for numbers between 0 and -9. For example, the fifth row of the table holds the numbers 1, 2, 4, 5, 5, 8, 9 and the sixth row holds 0, -6, -7, and -9. Values that are exactly 0 before rounding should be split as evenly as possible between the “0” and “-0” rows. In Table 2, none of the values are 0 before rounding. The “0” that appears in the “-0” row comes from the original value of -0.2 in the table.

Although stem and leaf displays are unwieldy for large data sets, they are often useful for data sets with up to 200 observations. Figure 5 portrays the distribution of populations of 185 US cities in 1998. To be included, a city had to have between 100,000 and 500,000 residents.

4|899 4|6 4|4455 4|333 4|01 3|99 3|677777 3|55 3|223 3|111 2|8899 2|666667 2|444455 2|22333 2|000000 1|88888888888899999999999 1|666666777777 1|444444444444555555555555 1|2222222222222222222333333333 1|000000000000000111111111111111111111111111

Figure 5. Stem and leaf display of populations of 185 US cities with populations between 100,000 and 500,000 in 1988.

Since a stem and leaf plot shows only two-place accuracy, we had to round the numbers to the nearest 10,000. For example the largest number (493,559) was 80