Quantile-Quantile and Probability Charts

Probability Chart

Normal Probability
  • In a normal probability chart, if the normal distribution adequately describes the data, the plotted points fall approximately along a straight line: see Model 4 in (a).
Uniform Probability
  • In a uniform probability chart, if the uniform distribution adequately describes the data, the plotted points fall approximately along a straight line (see Model 2 in the graph below).
Example Graphs

A Normal Probability Chart Displaying Data That Are Normally Distributed (Model 4) Compared to Data That Are Uniformly Distributed (Model 2)

Normal Probability

A Uniform Probability Chart Displaying Data That Are Uniformly Distributed (Model 2) Compared to Data That Are Normally Distributed (Model 4)

Uniform Probability