Page 49 - 2024-bfw-starnes-TPS7e-SE proofs.indd

36 UNIT 1 Exploring One-Variable Data

4. Adjust the intervals to match those in Figure 1.8(a), then graph the histogram. Press WINDOW and enter
the values shown for Xmin, Xmax, Xscl, Ymin, Ymax, and Yscl. Then press GRAPH. Press TRACE and use
the left and right arrow keys to examine the intervals.

AP® EXAM TIP
NORMAL FLOAT AUTO REAL RADIAN MP NORMAL FLOAT AUTO REAL RADIAN MP
© 2024 BFW Publishers PAGES NOT FINAL - For Review Purposes Only - Do Not Copy
Plot1:L1
WINDOW If you’re asked to make a graph
Xmin=0
Xmax=30 on a free-response question,
Xscl=5 be sure to label and scale your
Ymin= - 2
Ymax=22 axes. Don’t just transfer what
Yscl=2 you see on a TI-83/84 calcula-
Xres=1 tor screen to your paper and
^ X=0.11363636363636
TraceStep=0.227272727272... min=0 n=13 expect to earn full credit.
max<5
5. See if you can modify the graph so that it matches the histogram in Figure 1.8(b).

Don’t confuse histograms and bar graphs. Although histograms resemble bar
caution
graphs, their details and uses are different. A histogram displays the distribution
of a quantitative variable. Its horizontal axis identifies intervals of values that the
variable can take. A bar graph displays the distribution of a categorical variable.
Its horizontal axis identifies the categories. Be sure to draw bar graphs with blank
space between the bars to separate the categories. Draw histograms with no space
between the bars for adjacent intervals. For comparison, here is one of each type
of graph from earlier examples:

Histogram Bar graph
60
20 50

15 40
Frequency 10 Percentage of students 30

5 20
10
0 0 In person Internet Phone Social Text
0 5 10 15 20 25 30 chat/IM call media messaging
Percent foreign-born residents Preferred communication method

COMPARING DISTRIBUTIONS WITH HISTOGRAMS
Histograms can also be used to compare the distribution of a quantitative variable
in two or more groups. Be sure to use the same intervals when making compara-
tive histograms, so the graphs can be drawn using a common horizontal axis scale.
Mazie is interested in comparing the reading levels of a biology journal and an
airline magazine. To do so, Mazie counts the number of letters in a sample of 400
words from an article in the journal, and then counts the number of letters in a
sample of 100 words from an article in the airline magazine. Figure 1.9(a) displays
comparative histograms of the data. This figure is misleading — it compares fre-
quencies, but the two samples were of very different sizes (400 and 100).

© 2024 BFW Publishers PAGES NOT FINAL - For Review Purposes Only, all other uses prohibited - Do Not Copy or Post in Any Form.

02_StarnesTPS7e_40934_un01_p1_001_086_6pp.indd 36 13/09/23 5:37 PM