A fitted distribution line is a theoretical distribution curve calculated using parameter estimates derived from a sample or from historical values that you enter. Use fitted distribution lines to determine how well sample data follow a specific distribution. These distribution lines are usually overlaid with the actual data so that you can directly compare the empirical data to the hypothesized distribution.

You are investigating the strength of your company's product. As an initial step, you would like to determine whether your response data follow a normal distribution. To do this, you generate the following histogram with the fitted normal distribution.

The fitted normal distribution does not appear to be a good fit, as depicted by the histogram. There are more data than expected to the left of the peak and in the right tail.

The table on the graph displays the parameter estimates used to generate the curve.

A fitted distribution line appears by default, for example, on probability plots and empirical CDF plots. You can a fitted distribution line to these graphs and others, such as histograms.

- To add or edit a fitted distribution line when you create a graph, in the dialog box for the graph you are creating, click Distribution or Data View, and choose the Distribution tab.
- To add a fitted distribution line to an existing graph: right-click the graph and choose , or right-click the graph and choose .