Statistics: Averages and Graphs

Section 1Mean, median, and mode

The mean is the total divided by the number of values. The median is the middle value when the data is ordered. The mode is the value that occurs most often.

Section 2Frequency tables

A frequency table shows how often each value occurs. To find the mean from a frequency table, multiply each value by its frequency, add those products, then divide by the total frequency.

Section 3Grouped data

Grouped data is placed into class intervals such as 0-9, 10-19, and 20-29. For grouped data, use class midpoints when estimating the mean or drawing a frequency polygon.

Section 4Histograms

A histogram uses touching bars to show continuous grouped data. The horizontal axis shows class intervals, and the vertical axis usually shows frequency or frequency density.

Section 5Frequency polygons

A frequency polygon is drawn by plotting class midpoint against frequency and joining the points with straight lines. It is useful for showing the shape of a distribution.