Linear regression test of funnel plot asymmetry

Test result: t = -2.94, df = 20, p-value = 0.0080
Bias estimate: -2.0430 (SE = 0.6939)

Details:
- multiplicative residual heterogeneity variance (tau^2 = 2.0475)
- predictor: standard error
- weight:    inverse variance
- reference: Egger et al. (1997), BMJ