Suppose VATS procedures should be recommended for 25% surgeries, but historical data suggests they are used for only 20%. Using new data, your study will assess whether or not VATS rates have changed.
(a) A sample of size n = 54 recent lobectomy patients is easily available. What is the power of a 2-sided test based on only these patients?
(b) How large a sample is necessary for your study to achieve 90% power using a 2-sided test?