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Exploratory data analysis uses graphs and numerical summaries to describe the variables in a data set and the relations among them.

The distribution of a variable tells us what values it takes and how often it takes these values.

Bar graphs and pie charts display the distributions of categorical variables. These graphs use the counts or percents of the categories.

Stemplots and histograms display the distributions of quantitative variables. Stemplots separate each observation into a stem and a one-digit leaf. Histograms plot the frequencies (counts) or the percents of equal-width classes of values.