Describing Data

• Mean — add all values and divide by how many there are. Uses every value, but is pulled by outliers.
• Median — the middle value once sorted (average the two middle values if there's an even count). Resistant to outliers.
• Mode — the most frequent value. Useful for categorical data; a set can have none or several.

Which to use? Mean for roughly symmetric data; median when the data is skewed or has outliers (like incomes or home prices).

Range = maximum − minimum gives a quick sense of spread but ignores everything in between. Standard deviation measures the typical distance of values from the mean — a small standard deviation means the data is tightly clustered.

The shape matters too: data can be symmetric, right-skewed (a long tail of high values pulls the mean above the median), or left-skewed. For a deep visual reference with boxplots and Excel formulas, use the linked one-page summary below.