older than

older is used to restrict attention to a set of episodes ocurring at least a specified number of months prior to the current episode. For example, given the following case fragment:

           01 Jun 03    20 Jun 03    30 Jun 03    15 Oct 03    02 Nov 03
HDL           2.0          2.1          2.2          2.5          1.9
LDL                        6.2*         5.0*         3.5          3.9
Trig          3.0                                    1.9
LipidDrug     N                         Y            Y            N

some (LDL older than 3 months) is high

average HDL older than 3 months >= 2.1