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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.• When examining a distribution, look for

**shape, center**, and**spread**and for clear**deviations**from the overall shape.• Some distributions have simple shapes, such as

**symmetric**or**skewed**. The number of**modes**(major peaks) is another aspect of overall shape. Not all distributions have a simple overall shape, especially when there are few observations.•

**Outliers**are observations that lie outside the overall pattern of a distribution. Always look for outliers and try to explain them.• When observations on a variable are taken over time, make a

**time plot**that graphs time horizontally and the values of the variable vertically. A time plot can reveal changes over time.