Understanding Society User Support

Hi,

I have merged (appended) core individual variables from all UKHLS indresp waves a - k (1 - 11) longitudinally, and all waves of core household vars from hhresp longitudinally. Both files have data from all 11 waves.

But when I merge these longitudinal indresp with hhresp datasets many to one (m:1) on hidp, there is unmatched data from both the indresp and hhresp datasets, which I wasn't really expecting. (My code is good, I've done this before).

Can someone explain why this might be so that I understand what's going on with the data before I continue my analysis please? I.e. are there people who have answered the household questions (such as proxy respondents), but who have not completed the individual questionnaires?

Also if this is documented somewhere please can you direct me to where I can find the answers to this sort of question.

Many thanks for your help! Much appreciated!