We emphasize again that these coefficient estimates are valid only for a model with all three predictor Variables included. To better understand the accuracy of these effects, we construct conditional 95% con- dence intervals. For the estimated regression model there are (20-3-1) - 16 degrees of freedom for error. Thus, the Student's statistic for computing confidence intervalsis, from the Appendix, Iss - 2.12. The format for confidence intervalsts as follows: b; - *