The three steps necessary to define the classes for a frequency distribution with quantitative data are:
- Determine the number of nonoverlapping classes.
- 5~20 classes. (depends on the size of the data)
- Determine the width of each class.
- we recommend that the width be the same for each class.
- Approximate class width = Largest data value - Smallest data value / Number of classes (can be rounded for convenience)
- Determine the class limits.
(optional: class midpoint).
- Left/Right/Symmetric skew
(<= upper limit of each class)