The calculation of the out-of-pocket medical expenses variable, TRMOOPS, changed in the 2004 SIPP Panel compared to the way it was computed in the 2001 SIPP Panel. In the 2001 SIPP Panel, TRMOOPS was calculated as (TMDPAY+THIPAY)-TREIMBUR whereas in the 2004 Panel the calculation of TRMOOPS deleted the variable, THIPAY, from the calculation leaving TMDPAY-TREIMBUR. This difference causes TRMOOPS to be incomparable between the two panels. Data users who wish to construct comparable estimates between the 2001 and 2004 versions of TRMOOPS should calculate out-of-pocket medical expenditures by creating a recode variable that consists of (TMDPAY+THIPAY)-TREIMBUR.