Equal Interval
The range of data values between the minimum and maximum is divided into classes of equal length. For example, if 5 classes are used and the minimum data value is 0 and the maximum data value is 9, then each class will have a length of 2 and the classes will be 0-1, 2-3, 4-5, 6-7, and 8-9. Each class may have different numbers of values or no values.
Quantile
The same number of data values are placed into each class. For example, if 5 classes are chosen, then one-fifth (or 20%) of the values would be placed into each class. A class cannot ever be empty. It may not always be possible to divide the data into the specified number of classes if the data values are not varied enough.