EXAMPLE 10.21

Testing the slope. First we need the standard error of the estimated slope:

= 0.2516

To test

H₀: β₁ = 0

H_a: β₁ ≠ 0

calculate the t statistic:

Using Table D with n − 2 = 4 degree of freedom, we conclude that 0.02 < P < 0.04. The exact P-value obtained from software is 0.022. The data provide evidence in favor of a linear relationship between gestational age and umbilical cord diameter (t = 3.65, df = 4, 0.02 < P < 0.04).