In the past thirty years many social changes have taken place in Britain. The greatest of these have probably been in the economic lives of women. The changes have been significant, but, because tradition and prejudice can still handicap women in their working careers and personal lives, major legislation to help promote equality of opportunity and pay was passed during the 1970s. At the heart of women's changed role in society has been the rise in the number of women at work, particularly married women. As technology and society permit highly effective and generally acceptable methods of family planning there has been a decline in family size. Women as a result are involved in child-rearing for a much shorter time and related to this, there has been a rapid increase in the number of women with young children who return to work when the children are old enough not to need constant care and attention. Since 1951 the proportion of married women who work has grown from just over a fifth to a half. Compared with their counterparts elsewhere on the Continent, British women comprise a relatively high proportion of the work-force, about two-fifths, but on average they work fewer hours, about 31 a week. There is still a significant difference between women's average earnings and men's, but the equal pay legislation which came into force at the end of 1975 appears to have helped to narrow the gap between women's and men's basic rates. As more and more women joined the work-force in the 1960s and early 1970s there was an increase in the collective incomes of women as a whole and a major change in the economic role of large numbers of housewives. Families have come to rely on married women's earnings as an essential part of their income, rather than as 'pocket money'. At the same time social roals within the family are more likely to be shared, exchanged or altered. The general idea of the passage is about______.