Is the lot of female executives improving?

WALL STREET'S glass ceiling cracked at last on March 1st, as Jane Fraser took charge of Citigroup, becoming the first woman to head a big American bank. That cracking sound has also been echoing across the rest of America Inc. Last year Carol Tomé became boss of UPS, a package-delivery giant. In January Rosalind Brewer became only the third black woman ever to run a Fortune 500 company (Walgreens Boots Alliance, a pharmacy chain). A month later Thasunda Brown Duckett was picked to run TIAA, a b...