Table 3.
Key results of power calculations under base assumptions
| Outcome | Average cluster size (per measurement occasion) | Treatment effect (Δμ or OR) | Parameter in control group (SD) | Parameter in treatment group (SD) | ICC | Power |
| Consult completion time | 120 | Δμ=−0.10 | μ0=27.8 (44.3) | μ1=25.0 (44.3) | 0.25 | 0.800 |
| 120 | Δμ=−0.10 | μ0=27.8 (44.3) | μ1=25.0 (44.3) | 0.30 | 0.800 | |
| 60 | Δμ=−0.15 | μ0=27.8 (44.3) | μ1= 23.6 (44.3) | 0.25 | 0.845 | |
| 50 | Δμ=−0.15 | μ0=27.8 (44.3) | μ1=23.6 (44.3) | 0.25 | 0.775 | |
| 60 | Δμ=−0.15 | μ0= 27.8 (44.3) | μ1=23.6 (50.0) | 0.25 | 0.798 | |
| 70 | Δμ=−0.15 | μ0=27.8 (50.0) | μ1= 23.6 (50.0) | 0.30 | 0.812 | |
| Appointment completion time | 200 | Δμ=−0.05 | μ0= 60.0 (50.0) | μ1= 57.0 (50.0) | 0.20 | 0.930 |
| 140 | Δμ=−0.05 | μ0= 60.0 (50.0) | μ1= 57.0 (50.0) | 0.20 | 0.820 | |
| 300 | Δμ=−0.05 | μ0= 60.0 (75.0) | μ1= 57.0 (75.0) | 0.20 | 0.800 | |
| 110 | Δμ=−0.05 | μ0= 60.0 (50.0) | μ1= 57.0 (40.0) | 0.10 | 0.809 | |
| 240 | Δμ=−0.05 | μ0= 50.0 (50.0) | μ1= 47.5 (60.0) | 0.10 | 0.814 | |
| 400 | Δμ=−0.03 | μ0= 60.0 (50.0) | μ1= 58.2 (50.0) | 0.30 | 0.830 | |
| Travel distance (miles) | 550 | Δμ=−0.03 | μ0= 13.0 (13.0) | μ1= 12.61 (13.0) | 0.20 | 0.812 |
| 300 | Δμ=−0.04 | μ0= 13.0 (13.0) | μ1= 12.48 (13.0) | 0.20 | 0.800 | |
| 300 | Δμ=−0.04 | μ0= 13.0 (13.0) | μ1= 12.48 (13.0) | 0.10 | 0.801 | |
| 300 | Δμ=−0.04 | μ0= 13.0 (13.0) | μ1= 12.48 (13.0) | 0.30 | 0.800 | |
| 500 | Δμ=−0.04 | μ0= 13.0 (13.0) | μ1= 12.48 (20.0) | 0.20 | 0.814 | |
| 1000 | Δμ=−0.03 | μ0= 10.0 (12.0) | μ1= 9.70 (15.0) | 0.10 | 0.812 | |
| Proportion of teledermatology encounters | 1700 | OR=1.10 | p0=0.03 | p1=0.0329 | 0.05 | 0.809 |
| 500 | OR=1.10 | p0=0.20 | p1=0.2157 | 0.05 | 0.844 | |
| 500 | OR=1.10 | p0=0.03 | p1=0.1089 | 0.25 | 0.837 | |
| 450 | OR=1.20 | p0=0.03 | p1=0.0358 | 0.05 | 0.830 | |
| 150 | OR=1.20 | p0=0.10 | p1=0.1176 | 0.10 | 0.831 | |
| 200 | OR=1.30 | p0=0.03 | p1=0.0386 | 0.10 | 0.828 |
μ0 is the mean of the outcome variable in the control group; μ1 is the mean of the outcome variable in the treatment group; p0 is the proportion of interest in the control group; p1 is the proportion of interest in the treatment group; Δμ is the difference in means between the treatment and control arms, that is, the expected treatment effect to be detected for continuous outcomes; OR is the odds ratio between the treatment and control arms, that is, the expected treatment effect to be detected for the binary outcome.
ICC, intraclass correlation coefficient.