*! version 1.0.0 21Aug2021

Title

loasampsi -- power and sample size analysis for limits of agreement (LOA)

Syntax

loasampsi
mu
delta
, sd(#)
[
level(#)
power(#)
n(#) ]

mu is mean of differences and delta is maximum allowable mean difference between the two measurement methods; delta must be larger than the LOA.

sd(#) specify the expected standard deviation of the sample differences; sd() is required

level(#) set the confidence level; default is level(95)

power(#) specify the desired power; power() cannot be specified together with n()

n(#) specify the desired sample size; n() cannot be specified together with power()

Description

loasampsi computes sample size at a specified power, and power at a specified sample size, for Bland and Altman's (1986) limits of agreement (LOA) analysis,
according to the method developed by Lu et al. (2016).

The results produced by loasampsi are identical to those produced by the
PASS Sample Size Software
and the R package blandPower.

Options

sd(#) specifies the expecteded stardard deviation
of the sample differences; sd() is required.

level(#) specifies the confidence level, as a percentage, for
the limits of agreement. The default is level(95) or whatever is set by
set level.

power(#) specifies the desired power at which sample size is to be computed. The actual power
derived from the analysis is reported in the output. power() cannot be specified together with n().

n(#) specifies the desired sample size at which the power is to be computed. The actual power
derived from the analysis is reported in the output. n() cannot be specified together with power().

Examples

1) Computing sample size

Set the mean difference to 0.50, the delta to 7, the SD to 2.5, and power to 0.80.

. loasampsi .50 7, sd(2.5) power(0.80)

2) Computing power

Same as above but we specify n = 70 to find power at that sample size.

. loasampsi .50 7, sd(2.5) n(70)

Acknowledgments

I thank John Moran for testing this package.

Stored results

loasampsi stores the following in r():

Scalars

r(mu) mean of differences

r(delta) maximum allowable difference

r(sd) standard deviation of the difference

r(level) confidence level

r(power) actual power for the computed sample size

r(n) computed sample size

References

Bland, J. M., and D. G. Altman. 1986. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet I: 307-310.

Lu, M. J.,Zhong, W. H., Liu, Y. X., Miao, H. Z., Li, Y. C. and M. H. Ji. 2016. Sample Size for assessing agreement
between two methods of measurement by Bland-Altman method. The International Journal of Biostatistics
Article 20150039. (Published online).

Citation of loasampsi

loasampsi is not an official Stata command. It is a free contribution
to the research community, like a paper. Please cite it as such:

Linden A. (2021). LOASAMPSI: Stata module to compute power and sample size for limits of agreement (LOA) analysis

Authors

Ariel Linden

President, Linden Consulting Group, LLC

alinden@lindenconsulting.org

Also see

Online: rmloa (if installed)