This is a potentially very simple (and quite possibly silly) question, but its not one I've yet been able to fathom. When I extract the xwaveid dataset (in Stata 13) from SN6614, the pidp variable summary doesn't match that shown in the online documentation <www.understandingsociety.ac.uk/documentation/mainstage/dataset-documentation/wave/xwave/datafile/xwaveid/variable/pidp>
This seems to be because there are 27925 pidp cases where the pidp number is 0. According to the online summary, there shouldn't be any cases where pidp==0.
Is there something very obvious I am missing here?