Use the Knotted Spline Effect option to have JMP fit a segmentation of smooth polynomials to a specified effect. When you select this attribute, a window appears, enabling you to specify the number of knot points. (Knotted splines are only implemented for maineffect continuous terms.)
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Select Analyze > Fit Model.

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Click Run.

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From the report’s red triangle menu, select Estimates > Custom Test.

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Click the Add Column button twice to produce a total of three columns.

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In the first column, type 1 for age&Knotted@4.5.

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In the second column, type 1 for age&Knotted@20.5.

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In the third column, type 1 for age&Knotted@36.

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Click Done.

The report in Curvature Report appears. The small Prob > F value indicates that there is curvature.