I want to explain opera attendance, which is asked in July 2012 with total household income (HHINCOME), which is asked in ASEC yearly (in March). I can’t find id variables that allow me to merge the two. It seems to me that this should be doable, otherwise the non-March cps supplemental data can never be associated with total household income measured in dollars (not categories).
Unfortunately, due to the 4-8-4 sampling strategy of the CPS, it is very tricky to perform this match. This is largely because, households who are sampled in March will never be sampled in July. There are some non-March households included in the ASEC, but at the present time matching using MARCBASECID (more details here) is not possible. You can use income questions available through the Outgoing Rotation Group/Earner Study to link with July variables, but you should familiarize yourself with the sampling strategy of the Outgoing Rotation Group questions.
I hope this is helpful.