11.2.8 An article in Wood Science and Technology ["Creep in Chipboard, Part 3: Initial Assessment of the Influence of Moisture Content and Level of Stressing on Rate of Creep and Time to Failure" (1981, Vol. 15, pp. 125-144)] reported a study of the deflection (mm) of particleboard from stress levels of relative humidity. Assume that the two variables are related according to the simple linear regression model. The data follow:

1. Calculate the least square estimates of the slope and intercept. What is the estimate of 2? Graph the regression model and the data. 2. Find the estimate of the mean deflection if the stress level can be limited to 65%. 3. Estimate the change in the mean deflection associated with a 5% increment in stress level. 4. To decrease the mean deflection by one millimeter, how much increase in stress level must be generated? 5. Given that the stress level is 68%, find the fitted value of deflection and the corresponding residual.

11.4.10 Consider the data in Exercise 11.2.8 on y = deflection and x = stress level. 1. Test for significance of regression using = 0.01. What is the P-value for this test? State the conclusions that result from this test. 2. Does this model appear to be adequate? 3. Estimate the standard errors of the slope and intercept.

11.2.8 graph

x = Stress level (%):	54	54	61	61	68
y = Deflection (mm):	16.473	18.693	14.305	15.121	13.505
x = Stress level (%):	68	75	75	75
y = Deflection (mm):	11.640	11.168	12.534	11.224