Probability Plots
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Graph > Probability Plot

Use probability plots to help you determine whether a particular distribution fits your data or to compare different sample distributions.

Minitab calculates the cumulative distribution function (cdf) and associated confidence intervals based on parameters estimated from your data. (You can also provide historical parameters using distribution options.) Parameter estimates or historical parameters are displayed in an output table along with an Anderson-Darling (AD) goodness-of-fit statistic and associated p-value, and the number of observations.

If the distribution fits your data:

·    The plotted points will roughly form a straight line.

·    The plotted points will fall close to the fitted distribution line.

·    The Anderson-Darling statistic will be small, and the associated p-value will be larger than your chosen a-level. (Commonly chosen levels for a include 0.05 and 0.10.)

More

For more information on probability plots, see Understanding probability plots and  Method of obtaining plot points. Minitab also provides specialized probability plot functionality for work in quality control (Stat > Quality Tools > Individual Distribution Identification) and reliability / survival (Parametric distribution analysis).

To change the method used to calculate the plot points, choose Tools > Options > Individual Graphs > Probability Plots.

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