Empirical CDFs
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Graph > Empirical CDF

Use empirical cdf graphs to evaluate the fit of a distribution to your data or to compare different sample distributions. By default, graphs include an empirical cumulative distribution function (ecdf) of your sample data, and a fitted normal cumulative distribution function (cdf).

The stepped ecdf resembles a cumulative histogram without bars. Minitab plots the value of each observation against the percentage of values in the sample that are less than or equal to that value. In this respect, an ecdf is similar to a probability plot except both axes are linear, which can make interpreting the ecdf more intuitive. For help interpreting the ecdf, see Understanding Empirical CDF Graphs.

The fitted cdf is based on parameters estimated from your data. (You can also provide historical parameters using distribution options.) Use the fitted cdf to:

·    Evaluate how well the distribution fits your data.

·    Estimate population percentiles from your sample.

·    Evaluate the fit of historical parameters to your data.

Minitab also displays an output table containing the parameter estimates or historical parameters.

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