Table 2 Estimated sample sizes per group, based on different outcome measures. For function and symptoms, standard deviations are from the Maine Lumbar Spine study, with 3-month follow-up (roughly equal proportions treated surgically and non-surgically). Return to work proportion is based on a study by the Washington State Department of Labor and Industries.
Category | Measure | Hypothesized difference between groups | N/group, 2-sided alpha = 0.05, power = 0.80 |
|---|---|---|---|
Functional Status | Difference in change in Roland score (0–23 scale, SD = 7.37) | 2.5 points | 136 |
| Â | Â | 3.0 points | 95 |
Symptoms | Improvement in pain (1 = gone, 5 = same, 7 = much worse) (SD = 1.841) | 0.75 point | 94 |
| Â | Â | 1.0 point | 53 |
Return to Work | Proportion currently employed, if lower proportion is 0.40 | 0.15 | 173 |
| Â | Â | 0.20 | 97 |