Extended Data Table 5 Sample size calculations

From: Somatic CAG repeat expansion in blood associates with biomarkers of neurodegeneration in Huntington’s disease decades before clinical motor diagnosis

  1. Table showing approximate sample size estimates for clinical trials involving equal allocation to one treatment group and a placebo group, which were calculated based on observed HDGE group versus control longitudinal models. The group differences in longitudinal rates were converted to Cohen’s d effect sizes using within-group longitudinal standard deviations derived from estimated random effect variances. Assumed treatment effects were then defined as the percent slowing of the group difference in longitudinal rates multiplied by the assumed trial length. Treatment effect assumes a reduction in the difference in rate between the HDGE and control groups. Boundary-shift integral is used to measure the change in the caudate, brain and ventricles. Gray matter and white matter changes are generated by convolving baseline voxel-based morphometry-derived gray or white tissue maps with voxel-compression maps of within-participant change. Putamen change is measured by subtraction of baseline and follow-up MALP-EM segmentations. See Supplementary Methods for further details. CSF, cerebrospinal fluid; HDGE, HD gene expanded; NfL, neurofilament light.
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