Determining the intervals (official procedure!): 1.Decide on the number of classes – typically between 5 and 15 2.Determine class width: range / # of intervals 3.Find class limits 4.Make a tally mark for each data entry in the appropriate interval 5.Count tally marks in each interval (This is just one way to do it…) Hard and fast rules! 1.All intervals must be the same width 2.There must be no gaps between intervals 3.There must be no overlap between intervals

Shapes of Distributions Note: These are only approximated by real data

Skewed right histograms Frequency Histogram Relative Frequency Histogram Notice the squiggly mark

Rules: Starts at 0 on the lowest lower bound Cumulative frequency on the upper bounds Connect the dots

Book example of an ogive