Note 4:

Households in the IPUMS files occasionally include more than one head, wife, mother of head, or father of head, usually because of enumerator or data-entry error. Such cases are corrected in the IPUMS version of the data by means of a consistency checking program prior to assigning parentage. We encountered true polygamous marriages very rarely; where these could be identified, we assigned the wives a detailed relationship code identifying them as wives of a polygamous husband.