Two types of artificial knee are to be compared for range of motion, measured in degrees. Theoretically, either could give a greater range. A journal article on the first type of knee gave a sample mean of 112 degrees, with a standard deviation of 13 degrees, and an article on the second type gave a sample mean of 118 degrees with a standard deviation of 11 degrees. We want to perform a new randomized trial to decide whether a 6 degree difference is statis-tically detectable using a 5% significance level, and maintaining at least 90% power. We are willing to assume that the population standard deviation is somewhere between the sample standard deviations reported in the two articles. What is the minimum number of subjects receiving each type of knee (in a balanced design) we must record? Hint: Your answer should be a number, representing the number of subjects receiving a Type 1 knee (which will be equal to the number receiving a Type 2 knee).
Two types of artificial knee are to be compared for
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