http://www.icpsr.org/icpsrweb/ICPSR/studies/9836;jsessionid=5C778733263D9AE441544F58422017E2?classification=ICPSR.IV.B.
http://www.icpsr.org/icpsrweb/ICPSR/studies/3012;jsessionid=5C778733263D9AE441544F58422017E2?classification=ICPSR.IV.B.
http://www.icpsr.umich.edu/icpsrweb/ICPSR/studies/21741