Table 3.

Alternate strategies for presenting the effect on pain.

Effect on Postoperative PainEstimated Risk or Estimated Score/value with PlaceboAbsolute Reduction in Risk or Reduction in Score/value with DexamethasoneRelative Effect (95% CI)Comments
Standardized mean difference (SMD)The pain score in the dexamethasone groups was on average 0.79 SD (1.41 to 0.17) lower than in the placebo groupsAs a rule to thumb, 0.2 SD represents a small difference, 0.5 a moderate, and 0.8 a large.
Natural units (converted from SD units)Mean scores with placebo ranged from 43 to 54Mean scores in the dexamethasone groups was on average 8.1 (1.8 to 14.5) lowerThe MID on the 0 to 100 pain scale is about 10. Two possible statistical approaches, one relying on the SMD and the other on direct conversion of all instruments to units of the most familiar instrument.
Dichotomizing using “substantial postoperative pain” vs other20 per 100Difference in proportion achieving an important improvement is 0.15 (0.19 to 0.04)RR = 0.25 (0.05 to 0.75)Two possible statistical approaches, one going directly from SMD to risk difference and the other using the MID to calculate risk differences in individual studies and then pooling across studies.
Ratio of means28.13.7 lower pain score (6.1 to 0.6)ROM = 0.87 (0.78 to 0.98)The ROM is the weighted average of the mean pain score in the treatment groups divided by the mean pain score in placebo.
MID unitsThe pain score in the dexamethasone groups was on average 0.40 (0.74 to 0.07) MID units less than placeboAn effect of less than half the MID difference suggests a small or very small effect.
  • MID: minimally important difference; RR: risk ratio.