GWAS and the MTAG results to calculate how much larger the GWAS sample size would have to be to give a mean χ2-statistic equal to that attained by MTAG: NGWAS-equiv,j=NGWAS,jχMTAG2¯−1χGWAS2¯−1, where χGWAS2¯ is the mean χ2-statistic in the GWAS results and χMTAG2¯ is the mean χ2-statistic in the MTAG results. Put another way, conducting MTAG gives the same power (as measured by mean χ2-statistic) as conducting GWAS in sample size that is larger by a factor of χMTAG2¯−1χGWAS2¯−1.
