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Paper Information

Journal:   JOURNAL OF RESEARCH IN MEDICAL SCIENCES (JRMS)   May-June 2003 , Volume 8 , Number 2; Page(s) 11 To 16.
 
Paper: 

THE INFLUNCE OF CARRY-OVER EFFECT ON SAMPLE SIZE AND POWER OF THE.TEST IN 2X2 CROSS-OVER STUDY

 
 
Author(s):  SOLEYMANI B.*, FAGHIHZADEH S., KAZEMNEJAD ANOUSHIRAVAN, BABAEI G.H.
 
* Department of Biostatistics and Epidemiology, School of Health, Isfahan University of Medical Scienc, Isfahan,Iran
 
Abstract: 

The problem of carry-over effect in two period -two sequence cross-over studies has already brought about a lot of discussion and has induced to bring up different views and recommendations. The present study deals with relationship between carry-over effects and sample size in 2x2 cross-over design. It has been shown that when such effects exist, number of samples will differ from the case when there is no carry-over effect. The difference in sampel size has been estimated and has been shown that depends upon the differences in size and direction of carry-over effect and direct treatment effects.
 The influence of carry-over effects on power of the test also has been considered and its variation has been shown. The results suggest that while determining sampel size for a 2x2 cross-over study, it is matter of wise to take into account any knowledge about carry-over effect difference which is in hand from a previous or pilot study or even from a rational guess, especially if carry-over effects difference and direct treatment effects difference are in the same direction. Theoretical outcomes are used for a practical example and related results have been presented.

 
Keyword(s): 2X2 CROSS-OVER STUDY, SAMPLE SIZE, CARRY-OVER EFFECT
 
References: 
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