Frequency distribution
In
statistics, a
frequency distribution is a list of the values that a variable takes in a
sample. It is usually a list, ordered by quantity, showing the number of times each value appears. For example, if 100 people rate a five-point
Likert scale assessing their agreement with a statement on a scale on which 1 denotes strong agreement and 5 strong disagreement, the frequency distribution of their responses might look like:
| Rank | Degree of agreement!Number | | 1 | Strongly agree | 25 |
| 2 | Agree somewhat | 35 |
| 3 | Not sure | 20 |
| 4 | Disagree somewhat | 15 |
| 5 | Strongly disagree | 5 |
This simple tabulation has two drawbacks. When a variable can take continuous values instead of discrete values or when the number of possible values is too large, the table construction is cumbersome, if it is not impossible. A slightly different tabulation scheme based on the range of values is used in such cases. For example, if we consider the heights of the students in a class, the frequency table might look like below.
| Height range | Number of students!Cumulative Number | | 4.5 -5.0 feet | 25 | 25 |
| 5.0-5.5 feet | 35 | 60 |
| 5.5-6 feet | 20 | 80 |
| 6.0-6.5 feet | 20 | 100 |
|
Operating and managing on frequency tabulated data is much simpler than operation on raw data. There are simple algorithms to calculate median, mean, standard deviation etc. from this tables.
Statistical hypothesis testing is founded on the assessment of differences and similarities between frequency distributions. This assessment involves measures of
central tendency or
averages, such as the
mean and
median, and measures of variability or
statistical dispersion, such as the
standard deviation or
variance.
A frequency distribution is said to be
skewed when its mean and median are different. The
kurtosis of a frequency distribution is the concentration of scores at the mean, or how peaked the distribution appears if depicted graphically—for example, in a
histogram. If the distribution is more peaked than the
normal distribution it is said to be leptokurtic; if less peaked it is said to be platykurtic.
Frequency distributions are also used in
frequency analysis to crack codes and refer to the relative frequency of letters in different languages.
