IF(ABS(TINV(1-$D$5,A$11+B$11-2))<=ABS(A13-B13)/SQRT((A$11*A13+B$11*B13)/(A$11+B$11)*(1-(A$11*A13+B$11*B13)/(A$11+B$11))*(1/A$11+1/B$11)),IF(B13>A13,"A","")
上面的公式尤其不明白SQRT((A$11*A13+B$11*B13)/(A$11+B$11)*(1-(A$11*A13+B$11*B13)/(A$11+B$11))*(1/A$11+1/B$11))是算什么，请详细解释，这个是在算方差吗？