The article "Bone Density and Insertion Torque as Predictors of Anterior Cruciate Ligament Graft Fixation Strength" (The Amer. J. of Sports Med., 2004: 1421-1429) gave the accompanying data on maximum insertion torque (N · m) and yield load (N), the latter being one measure of graft strength, for 15 different specimens.

a. Is it plausible that yield load is normally distributed?
b. Estimate true average yield load by calculating a confidence interval with a confidence level of 95%, and interpret the interval.
c. Here is output from Minitab for the regression of yield load on torque. Does the simple linear regression model specify a useful relationship between the variables?

d. The authors of the cited paper state, "Consequently, we cannot but conclude that simple regression analysis based methods are not clinically sufficient to predict individual fixation strength." Do you agree?

Torque .8 2.2 1.9 1.3 2.1 2.2 1.6 2.1 Load 491 477 598 361 605 671 466 431 Torque |1.2 1.8 2.6 2.5 2.5 1.7 16 Load 384 422 554 577 642 348 446 Predictor Constant Torque S-73 . 2 14 1 R-Sg-53.6% R-Sq(adj )-50.0% Source Regression Residual Brror 13 69684 5360 Total Coef 152.44 178.23 SB Coef 91.17 45.97 1.67 3.88 0.118 0.002 DF MS 1 80554 80554 15.03 0.002 14 150238