Calculating Statistical Power

In Episode 67 of Med School Question of the Week for USMLE, Alisa Khomutova, MedSchoolCoach expert tutor, answers this medical school question: The height of Norwegian female adults is expected to follow a normal distribution, with a typical female adult having an above average height of 69 inches with a standard deviation of 0.1 inches. An investigator has been informed about a small population living in mountains greater than 10,000 feet above season level in which a lower mean height has been reported. The investigator plans to sample 30 female residents to test the claim that heights in this town differ significantly from the national average based on heights assumed be normally distributed. The significance level is set at 10% and the probability of a type 2 error is assumed to be 15%. Based on this information, which of the following is the power of the proposed study?

• 0.05
• 0.1
• 0.15
• 0.85
• 0.9