The numbers are stark - for the first time in India's recent history, not only there was a decline in the female labour participation rate, but also a shrinking of the total number of women in the workforce.
- Nearly 20 million Indian women quit work between 2004-05 to 2011-12
- The labour force participation rate for women of working age declined from 42% in 1993-94 to 31% in 2011-12
- Some 53% of the total drop - the largest chunk - happened among women aged 15-24 and living in villages
- In rural areas, the female labour force participation rate dropped from 49% to 37.8% between 2004-05 and 2009-10
- While more than 24 million men joined the work force between 2004-5 to 2009-10, the number of women in the the work force dropped by 21.7 million
Using data gleaned from successive rounds of National Sample Survey Organisation and census data, a team of researchers from World Bank have attempted to find out why this is happening.
"These are significant matters of concern. As India poises itself to increase economic growth and foster development, it is necessary to ensure that its labour force becomes fully inclusive of women," says the study, authored by Luis A Andres, Basab Dasgupta, George Joseph, Vinoj Abraham and Maria Correia.
So what accounts for the unprecedented and puzzling drop in women's participation in the workforce - at a time when India's economy has grown at a steady pace?
Predictable social norms are attributed to women quitting work in India: marriage, motherhood, vexed gender relations and biases, and patriarchy.
But they may not be the only reasons. Marriage, for example, does affect the rate of participation of women in the workforce. But in villages, the workforce participation rate of married women has been found to be higher than that of unmarried women - whereas in the cities, the situation is reversed.
Significantly, rising aspirations and relative prosperity may be actually responsible for putting a large cohort of women out of work in India.
Remember, the largest drop has been in the villages.
After calculating the labour force participation rates and educational participation rates (young women in schools) the researchers believe that one plausible explanation for the drop in the participation rate among rural girls and women aged 15-24 is the recent expansion of secondary education and rapidly changing social norms leading to "more working age young females opting to continue their education rather than join the labour force early".
The study says there has been a "larger response to income changes among the poor, rather than the wealthy, by sending children to school".
Also, casual workers - mainly women - drop out of the workforce when wages increased for regular earners - mainly men - leading to the stabilisation of family incomes.
"Improved stability in family income can be understood as a disincentive for female household members to join the labour force," says the study.
"This largely resonates with the existing literature, which suggests that with rising household income levels, women in rural India withdraw from paid labour and engage in status production at home."
But dropping or opting out of the workforce to go to school and get an education may not ensure that these women will eventually go to work.
After studying the relationship with the female labour participation rate and levels of educational achievements, the researchers found that having a high school-level education was "not found to be an incentive for women" to work.
The lowest rate of participation is among those who had secured school and high school education in the cities and villages. And the rate is actually highest among illiterates and college graduates.
But there has been a general drop in the rate in recent years, indicating that irrespective of educational attainments, "the incentive for women to participate in the workforce has declined over this period".
To be sure, India has a poor record of female participation in the workforce: the International Labour Organisation ranked it 121 out of 131 countries in 2013, one of the lowest in the world.
Also, India is not an outlier when it comes to women dropping out of the workforce.
Between 2004 and 2012, the female labour force participation rate in China dropped from 68% to 64%, but the participation rate remains very high compared with India. In neighbouring Sri Lanka, for example, the participation rate has dropped, but only by 2%.
"India stands out because of a such a sharp decline within such a short period. In levels, it is very low in international rankings now," the researchers told me.
Clearly women need better and more suitable job opportunities, outside agriculture. Rural labour markets need to offer jobs that are acceptable and attractive to women and their families.
The World Bank study suggests that gains will not be realised unless social norms around women's - and men's - work also change:
"Strategies to communicate the importance of women's work should take into account the roles of women, husbands and in-laws."
Also, as another study says, the "ongoing decrease in the availability of farm-based work, has led to women focusing on economic activities within their households". Should home-based workers then be counted as members of the labour force?