Page 314 - Statistics for Dummies

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Part V: Statistical Studies and the Hunt for a Meaningful Relationship
second variable). The marginal row totals form an additional column on the
right side of the table, and the marginal column totals form an additional row
on the bottom of the table.
For example, in Table 19-2 in the preceding section, the marginal row total for
row 1, the number of pet campers, is 20 + 10 = 30; the marginal row total for
non–pet campers (row 2) is 55 + 15 = 70. The marginal column total for those
wanting a pet section (column 1) is 20 + 55 = 75; and the marginal column
total for those not wanting a separate section (column 2) is 10 + 15 = 25.
The grand total is the total of all the cells in the table and is equal to the
sample size. (Note the marginal totals are not included in the grand total, only
the cells.) The grand total sits in the lower right-hand corner of the two-way
table. In this example, the grand total is 20 + 10 + 55 + 15 = 100. Table 19-3
shows the marginal row and column totals and the grand total for the pet
camping survey data.
The marginal row totals always sum to the grand total, because everyone
in the survey either camps with a pet or they don’t. In the last column of
Table 19-3 you see that 30 + 70 = 100. Similarly the marginal column totals
always sum to the grand total; everyone in the survey either wants a pet
section or they don’t; in the last row of Table 19-3 you see 75 + 25 = 100.
Table 19-3 Two-Way Table of Pet Camping Survey Data,
Including Marginal Totals
Support Separate Oppose Separate Marginal Row
Pet Section Pet Section Totals
Pet Camper 20 10 20 + 10 = 30
Non–Pet Camper 55 15 55 + 15 = 70
Marginal Column 20 + 55 = 75 10 + 15 = 25 Grand total =
Totals 100 (20 + 10 + 55
+ 15)
When organizing a two-way table, always include the marginal totals and the
grand total. It gets you off on the right foot when analyzing the data.
Interpreting Two-Way Tables

After the two-way table is set up (with the help of the information in the
previous section), you calculate percents to explore the data to answer your
research questions. Here are some questions of interest from the camping

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