This model performs Egger regression, a special case of the general method of meta-regression.11 15 Egger’s test for small study bias in meta-analysis assesses whether the intercept term β0E is different from zero. This will occur if the estimates from small studies (in the case of Mendelian randomization, estimates from weaker genetic variants) are more skewed towards either high or low values compared with estimates from large studies (stronger variants). The estimated value of the intercept in Egger regression β^0E can be interpreted as an estimate of the average pleiotropic effect across the genetic variants. An intercept term that differs from zero is indicative of overall directional pleiotropy.
