Flag for existence of a marriage for which date is unknown because it was not collected in the SIPP. The marital history topical module asks about a person's first and second marriages and then his or her most recent marriage. If any other marriages occurred after the second but before the most recent, no information about this marriage is collected. However, individuals are categorized as having 1, 2, 3, or more than 3 marriages. We create flag_mar4t to identify individuals who reported more than 3 marriages at the time of the topical module.

0	No additional marriage occurred with unknown date
1	An additional marriage occurred but with unknown date
Sysmiss