About percentile lines

Percentile lines are specialized reference lines available only with probability plots and empirical CDF plots. A percentile line has two segments that intersect at the fitted distribution line. One segment is drawn to intersect the data scale and the other is drawn to intersect the percent scale, probability scale, or score scale, depending on the option you have selected.

Percentile lines are often used for evaluations of test scores. For example, if you want to know the test score for the 95th percentile, you can add a percentile line at 95 percent. Minitab calculates the corresponding data value. Conversely, if you add a percentile line at the data value, Minitab calculates the corresponding percent.

95th percentile
Test score of 27
Example of using percentile lines to evaluate test scores

An employee ranking at the 95th percentile achieved a test score of 31.64. In other words, 95% of the employees had a score of 31.64 or less. A test score of 27 is slightly higher than the 70th percentile, or slightly more than 70% of the employees had a score of 27 or less.

Add percentile lines to a graph

You can add percentile lines to probability plots and empirical CDF plots.

  • To add percentile lines when you create a graph: in the dialog box for the graph you are creating, click Scale, click the Percentile Lines tab, and then specify the percentile line positions.
  • To add percentile lines to an existing graph: right-click the graph, choose Add > Percentile Lines, and then specify the percentile line positions.
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