Oftentimes a set of data covers a wide range of values,
making it unreasonable to list all of the individual potential
scores that a variable might take on when construcing a
frequency distribution table.
- Grouped Frequency Distribution Tables
- A grouped frequency distribution table has grouped X-value
intervals in place of individual X values. The
intervals correspond to a range of potential scores.
There are several rules that help guide you in constructing
a grouped frequency distribution table. These rules are
guidelines, not absolute requirements. The rules are:
- There should be about 10 class intervals.
- The width of each interval should be a "simple" number
(2, 5, 10, 20, etc.).
- The bottom score in each class interval should be a
multiple of the width.
- All intervals should be the same width.
Consider the scores in the following table:
Following the rules
given above, we construct the grouped frequency distribution
table shown at the right by using the following steps:
- We note that the maximum is 94 and the minimum is 53.
Thus we have a range of 94 - 53 + 1 = 42 potential scores.
- We divide this range into about 10 class intervals (rule
1), each of which is a "simple" number (rule 2). This
leads to 9 intervals with a width of 5 each.
- We make the bottom interval start at 50 since this is
the first number below the minimum that is a multiple
of the interval width (rule 3). The bottom inteval would
be 50-54, the next one 55-59, etc. This makes all intervals
the same width (rule 4).
Note that ViSta can construct frequency tables. Below
this text appears the table that comes closest to the one
that we did following the rules given above.
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|ViSta's Frequency Table for Example Scores