Week 2: Distribution of a variable
EXPLORING DATA
1. Begin by examining each variable by itself. Then move on to study the
relationships among the variables.
2. Begin with a graph or graphs. Then add numerical summaries of
specific aspects of the data.
The proper choice of graph depends on the nature of the variable. To
examine a single variable, we usually want to display its distribution.
DISTRIBUTION OF A VARIABLE
The distribution of a variable tells us what values it takes and how often
it takes these values.
The values of a categorical variable are labels for the categories. The
distribution of a categorical variable lists the categories and gives either
the count or the percent of individuals who fall in each category. (It tells
us which values a variable takes and in which frequencies.)
Distribution of categorical variables
Pie charts show the distribution of a categorical variable as a “pie”
whose slices are sized by the counts or percents for the categories. Pie
charts are awkward to make by hand, but software will do the job for
you. A pie chart must include all the categories that make up a whole.
Use a pie chart only when you want to emphasize each category’s
relation to the whole.
Bar graphs represent each category as a bar. The bar heights show the
category counts or percents. Bar graphs are easier to make than pie
charts and also easier to read.The bars can ber ordered alphabetically by
field of study (with “Other” at the end). Although it is often better to
arrange the bars in order of height. This helps us immediately see which
majors appear most often. Bar graphs are more flexible than pie charts.
