Linear regression test of funnel plot asymmetry

Test result: t = -1.47, df = 8, p-value = 0.1790
Bias estimate: -3.7911 (SE = 2.5740)

Details:
- multiplicative residual heterogeneity variance (tau^2 = 30.8369)
- predictor: standard error
- weight:    inverse variance
- reference: Egger et al. (1997), BMJ