Re: [Gretl-devel] NA*0? What about dummy variables?
On Sat, 17 Apr 2010, Lee Adkins wrote:
->OK, they may make _some_ distinction, but if they evaluate 0*NA
as-
->NA (as we've heard) then they are not doing it right.
Except if 0 is a dummy variable. In that case 0*NA = NA., 0 is
not really zero in ordinal data--it's arbitrary and just
indicates a category. Otherwise recoding the dummy variables
changes the effective data set and lead to unexpected results.
Good point. Just thinking it through: If one had (D1: female = 1,
male = 0) and (D2: married = 1, unmarried = 0), and for some
individuals D2 was NA, and then one created an interaction D1*D2,
one would wrongly categorize males of unknown marital status as
unmarried males, if 0*NA = 0. I'll have to think about that.
Allin