Histogram
A histogram is a bar graph representing a frequency distribution of a quantitative variable.
A histogram is made up of a vertical scale, which identities the frequencies in the various classes, and the horizontal scale, which identifies the independent variable.
Histograms are valuable tools. The histogram of the sample should have a distribution shape that is very similar to that of the population from which the sample was drawn.
The terms used to describe histograms are as follows:
Symmetrical: both sides of the distribution are identical.
Uniform: every value appears with equal frequency.
Skewed: One tail is stretched out longer than the other. The direction of skewness
is on the side of the longer tail.
Steps for creating a histogram:
1. Using the following data set, enter the data as List 1
(L1).
95 |
92 |
89 |
88 |
87 |
85 |
85 |
67 |
80 |
77 |
78 |
75 |
76 |
92 |
85 |
71 |
72 |
72 |
73 |
68 |
69 |
67 |
65 |
60 |
55 |
54 |
56 |
42 |
41 |
75 |
52 |
39 |
52 |
103 |
107 |
2. On the TI-82, press 
, 
,
and 
to setup Plot
1. Press to turn
on Plot 1. Press 
, 
, , , and to select the histogram plot. The Xlist (horizontal
axis) should be set for List 1 (L1) and the frequency set for 1.
On the TI-83, press , , and to setup Plot 1. Press to turn on Plot 1.
Press , , , and to select the histogram plot. The Xlist (horizontal
axis) should be set for List 1 (L1) and the frequency set for 1.
3. Set the viewing window for the histogram by pressing 
. From the menu, Xmin and Xmax control
the class boundaries, Xscl is the width of each class, Ymin should be set to 0 (the
minimum count in a frequency histogram), and Ymax should be at least the maximum frequency
of repeated data. You may have to experiment in order to find an appropriate value
for Ymax so that the entire histogram fits on the screen.
4. Press 
to see the histogram. With the settings at: Xmin = 25, Xmax
= 120, Xscl = 11, Ymin = -1, Ymax = 12, and Yscl = 1, the histogram should look like the
diagram below. 
Note: A value occurring on the edge of a bar is counted in the bar to the right.
5. An alternative way to adjust the viewing window is to press 
and 9:ZoomStat. This option
automatically adjusts the Xmin and Xmax to include all values, but does not change the
Xscl, which is the scale for the horizontal variable, Ymin, Ymax, or Yscl.
You can trace a histogram and use the arrow keys to move along the top center of each column. The calculator displays the class boundaries and the class frequency.