Power analysis
Only one study has measured GABA changes after ECT
by MRS in humans, and found an increase from 0.85
(SD =0.34) to 1.51 (SD =048) mmol/kg brain tissue,
N =8 [50]. Using a mean difference of 0.6 and a SD of
0.5, α =0.05 and power of 0.8 the total sample size
needed would be 8 (calculated using G*Power 3.1.3,
paired t-test, two-tailed).
For analysis of hippocampal volumes, data from
Nordanskog et al. [41] were used. For the right hippo-
campus the mean difference in volumes after a course
of ECT was 133 μL with a SD of 123 μL, similar analysis
as above indicates that the sample size needs to be at
least 9.
We found no studies on SWI and DWI imaging that
could be used to estimate power of the suggested study
protocol. Based on the analysis above, a total of 10
patients is a minimum. Due to wide inclusion criteria,
expected heterogeneity of the sample population and in
order to increase the robustness we intend to include
40 patients