"In some ways, determination of sample size is like buying a home; particularly when sample size is fixed. When you decide to buy a home and you can afford only $300,000, you may be able to buy a home with two bedrooms and a large living room, or a home with three bedrooms and a small living room. Likewise,if for financial or time constraints you can collect data from only 300 patients, that is what you can afford; with that you can get a small α and a large β, or a large α and a small β, or a small α and small β but a large d. You need to make sacrifices somewhere"