Refer to Exercise 7.S.15.
(a) Construct a 95% confidence interval for the difference in population means.
(b) Suppose the investigators believe that the effect of the low-chromium diet is "unimportant" if it shifts mean GITH activity by less than 15% - that is, if the population mean difference is less than about 8000 cpm/gm. According to the confidence interval of part
(a), do the data support the conclusion that the difference is "unimportant"?
(b) if the criterion were 4000 rather than 8000 cpm/gm?
(c) How would you answer the question in part.
Exercise 7.S.15.
In an investigation of the possible influence of dietary chromium on diabetic symptoms, 14 rats were fed a low-chromium diet and 10 were fed a normal diet. One response variable was activity of the liver enzyme GITH, which was measured using a radioactively labeled molecule. The accompanying table shows the results, expressed as thousands of counts per minute per gram of liver. Use a t test to compare the diets at α = 0.05. Use a non-directional alternative.

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Low-chromium diet Normal diet 53.1 53.6 50.7 47.8 55.8 61.8 42.3 51.5 53.7 58.5 48.0 55.4 56.038.3 55.754.1 54.8 52.1 52.8 51.3 47.5 53.7 55.7 383 55.1