Understanding Society User Support

Dear support team,

I have a question regarding the different sampling design used in Northern Ireland (NI). I am using nine waves of data from wave 'L' of the BHPS to USoc waves b and c (inclusive).

Given there are no PSUs or Strata in the BHPS for the NI sample, is there a recommended strategy for UK-wide analysis which includes NI? I note that for the Understand Society waves strata and PSUs are present for the NI sample. PSU seem to be set to be constant within household, and strata for the most part are '701' (though some are different for reasons I can't work out). I assume that it is not correct to follow this strategy for previous waves in the BHPS: assigning NI cases a PSU based on the household, and set strata to '701'? If this is incorrect, is a design based approach possible at all, or should I go with a model based approach?

Best wishes
David