Document Detail

How many do I need? Basic principles of sample size estimation.
MedLine Citation:
PMID:  15238124     Owner:  NLM     Status:  MEDLINE    
BACKGROUND: In conducting randomized trials, formal estimations of sample size are required to ensure that the probability of missing an important difference is small, to reduce unnecessary cost and to reduce wastage. Nevertheless, this aspect of research design often causes confusion for the novice researcher. AIM: This paper attempts to demystify the process of sample size estimation by explaining some of the basic concepts and issues to consider in determining appropriate sample sizes. METHOD: Using a hypothetical two group, randomized trial as an example, we examine each of the basic issues that require consideration in estimating appropriate sample sizes. Issues discussed include: the ethics of randomized trials, the randomized trial, the null hypothesis, effect size, probability, significance level and type I error, and power and type II error. The paper concludes with examples of sample size estimations with varying effect size, power and alpha levels. CONCLUSION: Health care researchers should carefully consider each of the aspects inherent in sample size estimations. Such consideration is essential if care is to be based on sound evidence, which has been collected with due consideration of resource use, clinically important differences and the need to avoid, as far as possible, types I and II errors. If the techniques they employ are not appropriate, researchers run the risk of misinterpreting findings due to inappropriate, unrepresentative and biased samples.
Declan Devane; Cecily M Begley; Mike Clarke
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Journal of advanced nursing     Volume:  47     ISSN:  0309-2402     ISO Abbreviation:  J Adv Nurs     Publication Date:  2004 Aug 
Date Detail:
Created Date:  2004-07-07     Completed Date:  2004-09-09     Revised Date:  2007-11-15    
Medline Journal Info:
Nlm Unique ID:  7609811     Medline TA:  J Adv Nurs     Country:  England    
Other Details:
Languages:  eng     Pagination:  297-302     Citation Subset:  IM; N    
School of Nursing and Midwifery Studies, University of Dublin Trinity College, Dublin, Ireland.
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MeSH Terms
Data Interpretation, Statistical
Nursing Research
Randomized Controlled Trials as Topic / methods*
Research Design
Sample Size*

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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