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Chapter 13: Forming Associations with Two-Way Tables
Notice that Table 13-1 has four empty cells inside of it (not counting the
empty space in the upper-left corner). Because gender has two choices (male
or female), and personal cell-phone use has two choices (yes or no), the
resulting two-way table has 2 2 = 4 cells.
*
To figure out the number of cells in any two-way table, multiply the number
of possible categories for the row variables times the number of possible
categories for the column variable.
Filling in the cell counts
After you set up the table with the appropriate number of rows and columns,
you need to fill in the appropriate numbers in each of the cells of the two-way
table. The number in each cell of a two-way table is called the cell count for
that cell. The upper-left cell in the two-way table shown in Table 13-1 repre-
sents the number of males who use their cell phones for personal calls. With
the information you have in the cell-phone problem, the cell count for this 211
cell is 325. Because you know that 427 females use their cell phones for per-
sonal calls, this number goes into the lower-left cell.
Now, to figure out the numbers in the remaining two cells, you do a bit of sub-
traction. You know from the information given that the total number of male
cell-phone users in the survey is 508. Each male either uses his cell phone for
personal calls (falling into the yes group), or he doesn’t (falling into the no
group). Because 325 males fall into the yes group, and you have 508 males
total, 183 males (508 – 325 = 183) don’t use their cell phones for personal
calls. This number is the cell count for the upper-right cell of the two-way
table. Finally, because 508 females took the survey, and 427 of them use
their cell phones for personal calls, you know that the rest of them (508 –
427 = 81) don’t. Therefore, 81 is the cell count for the lower-right cell of the
table. Table 13-2 shows the completed table for the cell-phone user problem,
with the four cell counts filled in.
Table 13-2 Completed Two-Way Table for the Cell-Phone Data
Personal Calls: Yes Personal Calls: No
Males 325 183 (508 – 325)
Females 427 81 (508 – 427)