Linear regression test of funnel plot asymmetry

Test result: t = -2.77, df = 12, p-value = 0.0171
Bias estimate: -1.6704 (SE = 0.6039)

Details:
- multiplicative residual heterogeneity variance (tau^2 = 1.4906)
- predictor: standard error
- weight:    inverse variance
- reference: Egger et al. (1997), BMJ