Structures built on a shallow foundation (e.g., a concrete slab-on-grade foundation) are susceptible to settlement. Consequently, accurate settlement prediction is essential in the design of the foundation. Several methods for predicting settlement of shallow foundations on cohesive soil were compared in Environmental & Engineering Geoscience (Nov. 2012). Settlement data for a sample of 13 structures built on a shallow foundation were collected. The actual settlement values (measured in millimeters) for each structure were compared to settlement predictions made using a formula that accounts for dimension, rigidity, and embedment depth of the foundation. The data are listed in the table.

a. What type of design was employed to collect the data?
b. Use the information in the accompanying SAS printout to construct a 99% confidence interval for the mean difference between actual and predicted settlement value. Give a practical interpretation of the interval.
c. Explain the meaning of "99% confidence" for this application.

Structure Actual Predicted ==2*=-23*2 1234567899- The TTEST Procedure Difference: ACTUAL - PREDICTED N Mean Std Dev Std Err Minimum Maximum | 13 0.4615 8.3528 2.3166 -14.0000 17.0000 Mean 95% CL Mean Std Dev 95% CL Std Dev 0.4615 4.5860 5.5091 8.3528 5.9897 13.7883 DF t Value Pr> It| 12 0.20 0.8454