Page 85 - Statistics for Dummies

Chapter 5: Means, Medians, and More
survey of 2,000 teenagers included 1,200 females and 800 males, the resulting
percentages would be (1,200 ÷ 2,000) ∗ 100% = 60% female and (800 ÷ 2,000) ∗
100% = 40% male.
You can break down categorical data further by creating something called
two-way tables. Two-way tables (also called crosstabs) are tables with rows
and columns. They summarize the information from two categorical variables
at once, such as gender and political party, so you can see (or easily calcu-
late) the percentage of individuals in each combination of categories and use
them to make comparisons between groups.
For example, if you had data about the gender and political party of your
respondents, you would be able to look at the percentage of Republican
females, Republican males, Democratic females, Democratic males, and so
on. In this example, the total number of possible combinations in your table
would be 2 ∗ 4 = 8, or the total number of gender categories times the total
number of party affiliation categories. (See Chapter 19 for the full scoop, and 69
then some, on two-way tables.)
The U.S. government calculates and summarizes loads of categorical data using
crosstabs. Typical age and gender data, reported by the U.S. Census Bureau for
a survey conducted in 2009, are shown in Table 5-1. (Normally age would be
considered a numerical variable, but the way the U.S. government reports it,
age is broken down into categories, making it a categorical variable.)
Table 5-1 U.S. Population, Broken Down by
Age and Gender (2009)
Age Both % Males % Females %
Group Sexes
Under 5 21,299,656 6.94 10,887,008 7.19 10,412,648 6.69
5–9 20,609,634 6.71 10,535,900 6.96 10,073,734 6.48
10–14 19,973,564 6.51 10,222,522 6.75 9,751,042 6.27
15–19 21,537,837 7.02 11,051,289 7.30 10,486,548 6.74
20–24 21,539,559 7.02 11,093,552 7.32 10,446,007 6.72
25–29 21,677,719 7.06 11,115,560 7.34 10,562,159 6.79
30–34 19,888,603 6.48 10,107,974 6.67 9,780,629 6.29
35–39 20,538,351 6.69 10,353,016 6.84 10,185,335 6.55
40–44 20,991,605 6.84 10,504,139 6.94 10,487,466 6.74
(continued)

3/25/11 8:17 PM
10_9780470911082-ch05.indd 69
10_9780470911082-ch05.indd 69 3/25/11 8:17 PM