Sample size calculations: should the emperor's clothes be off the peg or made to measure?
نویسندگان
چکیده
Conventional wisdom dictates that it is unethical to conduct a study that is so large that excess numbers of patients are exposed or so small that clinically important changes cannot be detected. This implies that there is some optimal sample size that can be calculated using statistical theory and information from previous research. But the choice of sample size is usually a compromise between statistical considerations, which always benefit from increased sample size, and economic or logistical constraints. Only rarely is sufficient information available to make informed decisions. Moreover, despite the illusion of precision that arises from the application of arcane statistical formulas, in many situations the choice of inputs—the expected treatment effect, the standard deviation, and the power—are subject to considerable uncertainty. As a result, sample size calculations may vary widely. We argue that, in the absence of good data, it would be better to determine sample size by adopting norms derived from historical data based on large numbers of studies of the same type. We show that for many common situations we can define defensible, evidence based, ranges of sample sizes. An example
منابع مشابه
Cut-off Sampling Design: Take all, Take Some, and Take None
Extended Abstract. Sampling is the process of selecting units (e.g., people, organizations) from a population of interest so that by studying the sample we may fairly generalize our results back to the population from which they were chosen. To draw a sample from the underlying population, a variety of sampling methods can be employed, individually or in combination. Cut-off sampling is a pr...
متن کاملImportant considerations in calculating and reporting of sample size in randomized controlled trials
Background: The calculation of the sample size is one of the most important steps in designing a randomized controlled trial. The purpose of this study is drawing the attention of researchers to the importance of calculating and reporting the sample size in randomized controlled trials. Methods: We reviewed related literature and guidelines and discussed some important issues in s...
متن کاملThe emperor's new clothes
bewildered by my first reading of Hans Christian Anderson's 'The Emperor's New Clothes'. It was a story book with pictures, and the emperor was drawn prancing down the street in underclothes befitting the Victorian era (I was amused to discover that in today's versions he is depicted stark naked). I was disappointed with the end of the tale, not being old enough for what is, in effect, a story ...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
- BMJ
دوره 345 شماره
صفحات -
تاریخ انتشار 2012