Fitted distribution lines

Select your graph below.

Probability plot

Use a fitted distribution line to assess how well sample data follow a specific theoretical distribution. By default, Minitab fits a normal distribution and estimates the parameters for the distribution from your sample. For information about distributions and parameters, go to Distributions for fitted lines.

For example, on the following probability plot, the middle solid line is the fitted normal distribution line.

To specify the distribution and parameters when you create a plot, click Distribution. On the Data Display tab, you can specify display options or change the confidence level for the confidence interval.

To add or remove the symbols or the fitted distribution line from an existing graph, click the graph and choose Editor > Add > Data Display. To change settings on an existing graph, double-click the fitted distribution line. On the Options tab, you can change the distribution, the distribution parameters, or the confidence interval. On the Attributes tab, you can change the line color, line size, or line type.

Confidence interval

By default, confidence intervals on a probability plot show the 95% confidence bounds for the individual percentiles of the distribution. These intervals form the outer solid lines on the plot, and can be used to assess the precision of the individual percentile estimates. The confidence intervals should not be used to assess the distribution fit.

Tip

Hold the mouse pointer on the fitted distribution line or on a confidence interval to view a table of estimated percentiles and their associated pointwise confidence intervals. To copy the tooltip text, select the element that has the tooltip, then choose Editor > Copy Text.

Empirical CDF plot

Use fitted distribution lines to assess how well sample data follow a specific theoretical distribution. By default, Minitab fits a normal distribution and estimates the parameters for the distribution from your sample. For information about distributions and parameters, go to Distributions for fitted lines.

For example, on the following empirical CDF plot, the red line is the fitted normal distribution line.

To specify the distribution and parameters when you create a plot, click Distribution. On the Data Display tab, you can specify whether to display the connect line, the fitted distribution line, or both.

To add or remove the connect line or the fitted distribution line from an existing graph, click the graph and choose Editor > Add > Data Display. To change the connect line or the fitted distribution line on an existing graph, double-click it. On the Attributes tab, you can change the line color, line size, or line type. On the Options tab for the fitted distribution line, you can change the distribution or the distribution parameters. On the Options tab for the connect line, you can change the connection function. For more information, go to Connect line.

Tip

Hold the mouse pointer on the fitted distribution line to view a table of estimated percentiles. To copy the tooltip text, select the element that has the tooltip, then choose Editor > Copy Text.

Histogram

Use a fitted distribution line to assess how well sample data follow a specific theoretical distribution. By default, Minitab fits a normal distribution and estimates the parameters for the distribution from your sample. For information about distributions and parameters, go to Distributions for fitted lines.

For example, the following histogram includes a fitted normal distribution line.

To specify a different distribution or enter distribution parameters when you create a graph, click Data View, then click the Distribution tab. To add a fitted distribution line to an existing graph, click the graph and choose Editor > Add > Distribution Fit. To change options on an existing graph, double-click the fitted distribution line. On the Options tab, you can change the distribution or the distribution parameters. On the Attributes tab, you can change the line color, line size, or line type.

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