Similar to the inverse variance weighted (IVW) method with fixed effects in concept, but all single nucleotide polymorphisms (SNPs) are weighted equally.
The intention of the method is that in some cases a genome-wide association study (GWAS) will return one extremely large effect on the exposure and many small effects, and that single large effect will dominate the analysis. The method is seldom used in practice though, as alternative approaches such as leave-one-out analysis can be used as sensitivity analysis instead.