According to the Sample Registration System (SRS) report of 2013, 13.1% of Tamil Nadu's married and divorced, widowed, or separated women are living separately, most of which are in rural areas. In contrast the report says only 2.5% of married men in the state are without a partner. In comparison just 5.2% of the entire married population in the country is single, of these 2.5% are men and 8.3% are women. Experts say a reason for the state's statistic is the age gap between the couples, with the husband being around six years older and likely dying before the wife, leaving her widowed. Another reason is said to be that female life expectancy is longer that male life expectancy, a conclusion arrived at as less than 1% of the single women are divorcees. Migration is also a reason for the situation as many men leave their homes in search of work in distant cities and do not return home, deserting their families. Three other southern states, Karnataka, Kerala and Andhra Pradesh also show a similar trend. The SRS is the largest demographic survey in the world covering some 1.5 million households and 7.52 million people.