Exercise: Head circumference, sex, and height, answer 8

Question 8: How could we check the assumption of linearity?

Suggested answer

We can check the assumption of linearity by adding a height squared term:

Head (mm) = 94.7 + 0.449×height (mm) - 0.000104×height squared (mm²) + 7.23×sex
95% CI -621.9 to 811.4 -0.389 to 1.287 -0.000349 to 0.000142 -0.70 to 15.12
P=0.8 P=0.3 P=0.4

In tabular form, the coefficients are:

Predictor Coefficient P 95% CI
intercept 94.7 0.8 -621.9 to 811.4
height 0.449 0.3 -0.389 to 1.287
height squared -0.000104 0.4 -0.000349 to 0.000142
sex 7.23 0.07 -0.70 to 15.12

Predictor	Coefficient	P	95% CI
intercept	94.7	0.8	-621.9 to 811.4
height	0.449	0.3	-0.389 to 1.287
height squared	-0.000104	0.4	-0.000349 to 0.000142
sex	7.23	0.07	-0.70 to 15.12

Continue with Exercise: Head circumference, sex, and height.

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Last updated: 20 March, 2006.