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Distribution Fitting Help

This page shows how to use the distribution fitting in SPC for Excel. The SPC for Excel program fits data to different distributions using the maximum likelihood estimation approach. When there are no direct solutions to the equations, Solver is used to find a solution that minimizes the log-likelihood function subject to constraints on the parameters. SPC for Excel fits the following distributions:

The distributions are defined by one or more of four parameters:

Running the Distribution Fitting

Distribution Fitting Output

If more than one distribution is fitted, a worksheet named “Summary” is added to the workbook. The top part of this sheet contains the descriptive statistics for the original data. The results for the distribution fitting are then provided.

Each distribution is listed. Each distribution is a link that takes you to the worksheet containing the results for that distribution. The following are given for each distribution:

Clicking on one the distributions, takes you to the worksheet for that distribution results. The top part of the worksheet contains the name of the distribution, the descriptive statistics for the original data, the distribution results as explained above and a link to return to the summary.

The bottom part of the worksheet contains the histogram of the data with the distribution superimposed and the P-P plot. If the points on the P-P plot lie along the straight line, the distribution fits the data.

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