Grouped Frequency Distributions:
Guidelines for classes:
A) There must be between 5 to 20 classes.
B) The class width must be an odd number. This will assure that the class mid-points are integers rather than decimals.
C) The classes should be mutually exclusive. This signifies that no data value can drop into two distinct classes.
D) The classes should be all exhaustive or inclusive. This signifies that each and every data values should be involved.
E) It can be kept in mind that classes will be continuous. There are no gaps in the frequency distribution. The classes which have no values in them should be involved
F) The classes should be equivalent in width. The exception here is the initial or last class. This is possible to have a "below ..." or "... and above" class. This is frequently used with ages.