The study to be published in the medical journal Lancet on Tuesday says the decline in the numbers of girls is larger in richer and better-educated households. It says a 1996 law that bans revealing the gender of a fetus has been largely ineffective.

Raw data from India's most recent census released in March showed 914 girls under age 6 for every 1,000 boys. A decade ago, many were horrified when the ratio was 927 to 1,000. The study says that selective abortions of girls are estimated at between 4 and 12 million between 1980 to 2010.