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.

The percentile lines on the following probability plots show that an employee who ranks 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. Also, a test score of 27 is slightly higher than the 70th percentile. In other words, slightly more than 70% of the employees had a score of 27 or less.

95th percentile
Test score of 27

To add percentile lines when you create a graph, click Scale. To add percentile lines to an existing graph, click the graph and choose Editor > Add > Percentile Lines.

To edit a percentile line, double-click it. On the Attributes tab, you can change the color, size, or line type. On the Show tab, you can specify whether to display a label on the x scale, the y scale, or both.

Labels

By default, a percentile line includes a label on the x-axis and a label on the y-axis. The first time you click one of the labels, both labels are selected. Click the same label again to select only that label. (For more information, go to Select groups and single items on a graph.)

To edit both labels for a percentile line, select both labels and then double-click. On the Font tab, you can change the size, color, style, or font of the labels. On the Show tab, you can choose to display the x-scale label, the y-scale label, or both.

To edit only the x-scale label or only the y-scale label, select the individual label and then double-click. On the Font tab, you can edit the text of the label and change the font, color, style, or size of the label. On the Alignment tab, you can use the following options to change the position and orientation of the label.

Tip

You can also click and drag to move a label.

Text angle
Rotate the labels. For example, rotating the labels on this time series plot by 35 degrees makes it easier to read adjacent labels.
Text angle = 0 (default)
Text angle = 35
Position
Change the position of the label relative to the anchor point. Under Position, choose Custom, then choose a position. The following examples show 3 of the available positions.
Above (default)
Above, to the left
Below, to the right
Offset
Move the label horizontally or vertically relative to its current position. Under Offset, choose Custom, then specify the horizontal or vertical distance to move the label.
Horizontal 0, Vertical 0 (default)
Horizontal –0.05, Vertical –0.05
Horizontal 0.05, Vertical 0.05
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