Grafen & Hails: Modern Statistics for the Life Sciences 
Datasets and supplementsGrafen & Hails: Modern Statistics for the Life Sciences
25.05.03 Eric Stolen, Dynamac Corp., Kennedy Space Center, USA
25.05.03 Eric Stolen, Dynamac Corp., Kennedy Space Center, USA Chapter 04, page 73
Q: In the answer to the first exercise in chapter 4 (The cost of reproduction) you use 24 degrees of freedom for the first confidence interval and 23 for the second. However, on page 33 you state that the degrees of freedom for the critical t-value are always the error degrees of freedom. Is there an error in the answer?
A: Indeed Eric is right and these answers are wrong. The degrees of freedom should be 23 and 22 instead of 24 and 23. The list of errata available on the website gives the correct answers as follows:
Page 289. The answer to (1) should read
The 95% confidence interval for the slope of LLONGVTY on LEGGRATE is 0.2813 ± t23 * 0.1165 = 0.2813 ± 0.2410 = (0.0403, 0.5223)
Page 290. The answer to (2) should read
The 95% confidence interval for the slope of LLONGVTY on LEGGRATE when size has been eliminated is -0.2899 ± t22 *0.0996 =-0.2899 ±0.2066 = (-0.4955, -0.0833)
These should be corrected in the second printing.
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