India - Housing Condition and Migration Survey: NSS 49th Round, Schedule 1.2, January - June 1993 

The households with at lest one out-migrant during the last 5 years (who was formerly a member of the household and currently living ) or an immigrant ( who is presently a member of the household ) but migrated ( in or out ) for employment or education will constitute second-stage stratum 1 while the remaining households will constitute second-stage stratum 2.
2. For the purpose a person is to be considered immigrant if his/her place of enumeration is different from his/her last usual residence, if any. The usual residence ( for the purpose of the survey ) is defined as a place ( village / town where the person has stayed continuously for a period of six months or more. Similarly , a former member will be considered as out-migrant if he/she is staying elsewhere i. e. in another village / town other than the one under survey.