Figure 3
From: A framework to assess the impact of number of trials on the amplitude of motor evoked potentials
Experimental validation of Eq. (11). (A) Estimations based on data from Experiment 1 to calculate the number of trials needed to detect a difference in MEP amplitude between 110%RMT and 120%RMT. (B) With the numbers from (A), Eq. (11) determines that to detect a significant difference using 10 (or 30) trials in a within-subjects design it would require 10 (or 7) subjects, whereas in a between-subjects design it would require 18 (or 16) subjects. \(\alpha \) = 0.05, \(\beta \) = 0.20 (i.e. \({z}_{\text{1} - \alpha \text{/2}}+ {z}_{{1}-\beta }\) = 2.80). (C) Experimental validation of predictions made by Eq. (11) on MEP amplitude (mV) measured at two different intensities (110%RMT and 120%RMT) for a within-subjects design with 10 trials per TMS intensity and 16 subjects. The session was repeated twice (Experiment 2). Each colored line represents a single subject. Paired t-test; **p < 0.01; ***p < 0.001. (D) Same as in (C) assuming a between-subjects design (i.e. two groups of 16 subjects), showing expected lower statistical power. Results are shown as box plots (horizontal lines: median (Q2), first quartile (Q1) and third quartile (Q3); whiskers: minimum and maximum value excluding outliers; outliers: points larger than Q3 + 1.5(Q3–Q1) or smaller than Q1–1.5(Q3–Q1). Unpaired t-test; *p < 0.05.
