Variance and correlation patterns
We estimated that the SI measured a clinically significant mean difference change of 0.06 as clinically significant. The variance of the difference between time 0 and time 1 was estimated to be 0.0097 based on a previous study conducted by Borovac and colleagues.25 We used this variance of difference as an estimate for the variances of the SI measures within subjects. Based on the previous data, with a specified minimal change in SI, a mean difference of 0.06 between the SI measures was considered clinically significant. A sample size of 252 patients per group, or a total of 504 patients, would give a power of at least 0.8 for testing the hypothesis.30.
The sample size estimation for the longitudinal analysis was performed using the General Linear Mixed Model Power and Sample Sizesoftware GLIMMPSE (URL: http://glimmpse.samplesizeshop.org/). All other analyses were performed using the R statistical software package (version 4.0.3). This report was written following the Enhancing the QUality and Transparency of Health Research (EQUATOR) STROBE guidelines.