Consider the Physicians’ Health Study data presented in Example 10.37 (p. 411).
How many participants need to be enrolled in each group to have a 90% chance of detecting a significant difference using a two-sided test with α = .05 if compliance is perfect?
Find the number of participants need to be enrolled in each group to have a 90% chance of detecting a significant difference using a two-sided test with α = 0.05 and compliance is perfect.
Answer to Problem 1P
The number of participants need to enrol in each group to achieve 90% power is 18,469.
Explanation of Solution
From Example 10.37, it is known that
Where,
From the given information, it is known that
Step-by-step procedure to obtain critical value using Excel:
- In an empty cell of an Excel sheet, type “=NORMSINV(1-(0.05/2))”.
- Click Enter.
The output obtained is as follows:
Thus,
Similarly, the value of
It can be written às follows:
Using Equation 10.13, the sample size is computed as follows
Thus, the number of participants need to enrol in each group to achieve 90% power is 18469.
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Chapter 10 Solutions
Fundamentals of Biostatistics
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