Normal Distribution

To plot this data, we construct a histogram and connect the midpoints of the resulting bars.  This gives us a plot of the distribution of the frequency of scores or, as it is usually named, the frequency distribution.

Frequency Distribution Diagram

Most biological systems, including the human, are "normally" distributed.  That is, when the frequency of occurrence of a specific attribute or characteristic is determined and graphed, the resulting graph will be a "normal" curve, also termed a "bell-shaped" curve or Gaussian distribution.  Data points are normally, (that is, in a regular manner) distributed about the mean (the average).

Many statistical tests assume that data is "normally" distributed about the mean, that we are indeed testing one population, and that there are no other variables within this population confounding our findings.