Table 1. Variance comparison.
Alternative possible methods for estimating the number and percentage of studies with different variances on comparisons between arms and over-time. Limits for declaring different variances come from different statistical methods: (1) the analysis relying on random-effects model and funnel plots; (2) the heuristic analysis based on number of studies that have to be deleted from the random-effects model in order to achieve a negligible heterogeneity (studies with larger discrepancies in variances were removed one by one until the estimated value of τ was as close as possible to that of the reference model – the one that compares the variances of the response at baseline. See Methods for details); (3) classic statistical tests for comparing variances (F for independent outcomes or Sachs’ test 21 for related samples). ¥ This comparison was performed on studies reporting enough information to obtain the variability of the change from baseline to outcome, for example because they provide the correlation between outcome and baseline values.
| Comparing
variances |
N | Method | After treatment, variability is… | ||
|---|---|---|---|---|---|
| Increased
n (%) |
Decreased
n (%) |
Not changed
n (%) |
|||
| Outcome between
treatment arms |
208 | Random-effects
model |
14(6.7%) | 26 (12.5%) | 168(80.8%) |
| Heuristic | 11 (5.3%) | 19 (9.1%) | 178 (85.6%) | ||
| F-test | 15 (7.2%) | 26 (12.5%) | 167 (80.3%) | ||
| Outcome versus
baseline in treated arm |
95 ¥ | Random-effects
model |
16 (16.8%) | 22(23.2%) | 57(60.0%) |
| Heuristic | 13 (13.7%) | 19 (20.0%) | 63 (66.3%) | ||
| Paired test | 16 (16.8%) | 22 (23.2%) | 57 (60.0%) | ||