This difficulty is not limited to the use of means. Bright and Friel (1998)
questioned 13-year-old students about a stem-and-leaf plot that showed the heights
of 28 students who did not play basketball. They then showed them a stem-and-leaf
plot that included these data along with the heights of 23 basketball players. This
latter plot is shown in Figure 2. Heights of basketball players were indicated in bold
type, as they are here. Students had learned how to read this type of display and had
no difficulty reading values from it. Asked about the “typical height” in the single
distribution of the non–basketball players, the students responded by specifying
middle clumps (e.g., 150–160 cm), a reasonable group summary. Yet, shown the
plot with both distributions, they could not generalize this method or find another
way to determine “How much taller are the basketball players than the students who
did not play basketball?”
This difficulty is not limited to the use of means. Bright and Friel (1998)questioned 13-year-old students about a stem-and-leaf plot that showed the heightsof 28 students who did not play basketball. They then showed them a stem-and-leafplot that included these data along with the heights of 23 basketball players. Thislatter plot is shown in Figure 2. Heights of basketball players were indicated in boldtype, as they are here. Students had learned how to read this type of display and hadno difficulty reading values from it. Asked about the “typical height” in the singledistribution of the non–basketball players, the students responded by specifyingmiddle clumps (e.g., 150–160 cm), a reasonable group summary. Yet, shown theplot with both distributions, they could not generalize this method or find anotherway to determine “How much taller are the basketball players than the students whodid not play basketball?”
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