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

3.0 points

95

Symptoms

Improvement in pain (1 = gone, 5 = same, 7 = much worse) (SD = 1.841)

0.75 point

94

1.0 point

53

Return to Work

Proportion currently employed, if lower proportion is 0.40

0.15

173

0.20

97


Deyo et al. BMC Musculoskeletal Disorders 2005 6:24   doi:10.1186/1471-2474-6-24

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