It can be seen from this comparison that the scores on Quiz #1 (on the left) were generally higher than
for those on Quiz #2—there are a lot more scores at the upper end. Although both distributions are
reasonably symmetric, the one on the left is skewed somewhat toward the smaller scores, and the one on
the right is skewed somewhat toward the larger numbers.
[Note: Most calculators do not have a built-in function for drawing stemplots. However, most
computer programs do have this ability, and it’s quite easy to experiment with various stem increments.]
Histogram
A bar graph is used to illustrate qualitative data, and a histogram is used to illustrate quantitative data.
The horizontal axis in a bar graph contains the categories, and the vertical axis contains the frequencies,
or relative frequencies, of each category. The horizontal axis in a histogram contains numerical values,
and the vertical axis contains the frequencies, or relative frequencies, of the values (often intervals of
values).
example: Twenty people were asked to state their preferences for candidates in an upcoming
election. The candidates were Arnold, Betty, Chuck, Dee, and Edward. Five preferred Arnold,
three preferred Betty, six preferred Chuck, two preferred Dee, and four preferred Edward. A
bar graph of their preferences is shown below:A histogram is composed of bars of equal width, usually with common edges. When you choose the
intervals, be sure that each of the datapoints fits into a category (it must be clear in which class any given
value is).