Determining The Sample Size In Agreement Studies

Let`s go back to the frequently asked questions about the design and analysis of measurement studies. 15. Zhou YH, Zang JJ, Wu MJ, Xu JF, He J. Total Errors and Incorrect Results Limits (ATE/LER) Areas for Measuring Agreement. J Clin Lab Anal 2011;25:83-89. Bland indicated the sample size for a study of the match between two measurement methods available on its website [9]. In the 1986 launch document, they indicated a 95% confidence interval formula for agreements. The typical error of the 95% chord added to root 3s2/n, where there is the standard deviation between the measurements using the two methods and n the sample size. The confidence interval is the estimate of the limit value, d- plus or minus 1.96s, plus or minus 1.96 standard error, and the sample size can be identified. 19. McAlinden C, Khadka J, Pesudovs K. Statistical methods for reaching agreements (comparison of clinical trials) and precision studies (repeatability or reproducibility) in optometry and ophthalmology.

Ophthalmological Physiology Opt 2011;31:330-338. We set α-0.05, β 0.20, μ 0.4 0.4, δ -2.7 and predetermined power – 80%. Figure 2 shows the sizes and strengths of the B-A sample and the new method under different parameter parameters. For the Bland-Altman method, the sample size is calculated without taking into account the effectiveness of the statistical method, so the probability of obtaining the required width is only 0.50. With the new method, the resulting performance is generally close to 80% performance. Recently, studies on the agreement between two instruments or clinical trials in the ophthalmological literature have multiplied. McAlinden et al. used a method of calculating sample size for agreement studies based on the method proposed by Bland [19]. The sample size was calculated without taking into account the effectiveness of the statistical method, so the probability of obtaining the required width was only 0.50 [20].

During the study phase, consideration of performance in sample size calculations could result in expected conclusions below the pre-established level of performance. Cesana et al. provided another estimate of sample size that was needed to establish a pearson correlation coefficient between the differences and the means of the measurements [20], and we feel that this method is not appropriate. Indeed, the correlation coefficient indicated by Cesana reflected proportional distortion. As we know, one of the hypotheses of application of the Bland-Altman method is not a proportional bias. In the absence of the hypothesis, this method would not be applicable. 5. Bland JM, DG Altman. Correct statistics: analyses of measurement studies.

Ultrasons Obst Gyn 2003;22:85-93.