Combining USOC/BHPS and zero weights
I have a couple more very small queries following on from our analysis; these are mainly for re-assurance that we’ve done things correctly.
1) With regard to the Youth data, is it ok to combine BHPS and USOC? We couldn’t find a combined weight but assumed this was still ok given that it’s done for adults. Therefore, when I created my weights (for w2/4 and w2/6), I started off by combining the weights thus (after checking the overlap):
- select cases with a non-zero weight for USOC or BGPS.
sele if not (b_ythscus_xw =0 and b_ythscbh_xw =0).
- calculate weight (wt) as either USOC weight or BHPS weight.
if wt=0 samptype=1.
if wt=0 wt=b_ythscbh_xw.
Val labels samptype 1 “BHPS” 2 “USOC”.
I then re-scaled the weights to average 1 within samptype and went on to model response to wave 4/6 contingent on wave 2, using interactions with samptype (USOC/BHPS) to take account of possible differences in response process between the two surveys. If it’s not ok to combine USOC and BHPS then my weights should still be fine given the way I’ve done them but it’d be helpful to know whether or not it’s ok to do so.
2) In the adult data, there seem to be many zero weights, more than we expected. We’d like to know if these are mainly related to students living in halls and other institutional addresses? E.g. among wave 5 fully productive interviews, the following syntax:
SELECT IF e_outcome = 11.
yields 4,481 cases with 0 value for e_indinub_xw (cross-sectional adult main interview weight for USoc & BHPS samples).
Many thanks for your help.
Updated by Peter Lynn over 5 years ago
- Target version set to X M
- % Done changed from 10 to 80
Re. point 1), this all looks broadly fine to me. The only caveat is that the two sets of weights for the different samples are designed to represent slightly different populations. The BHPS weights represent the UK population excluding any households consisting solely of people who entered the country since 2001 or are descended from such immigrants, while the UKHLS weights represent the UK population excluding any households consisting solely of people who entered the country since 2009 or are descended from such immigrants. In principle, one should up-weight the UKHLS post-2001 immigrant households to compensate for their absence in BHPS (this is exactly what we do in the “ub” weights), but I’m not sure how much difference this would make in practice.
Re. point 2), zero weights will arise whenever a household does not contain any adult who has been enumerated at every wave since the relevant start point (wave 2 in the case of “ub” weights; wave 1 for “us” weights). This is because the xw weights are derived from the lw weights and you need at least one person to have a non-zero lw weight in order for it to be shared to the other household members.
Updated by David Hussey over 5 years ago
Many thanks for the reply. I have a couple of follow-up questions re point (1):
1) May I just clarify that there isn't a ub weight for the Youth data?
2) The respsective profiles of w2 youth participants weighted by the two weights - b_ythscus_xw and b_ythscbh_xw - are rather different, which is partly why I queried the method I used to combine them. E.g. the aren't any 10 year olds in the BHPS sample (just 11-15 year olds), the proportion in owner occupied tenures is 8 ppts higher in the BHPS sample compared to the USOC sample and the proportion in urban areas is around 6 ppts lower. Given that the two are meant to be representing very similar populations the differences look rather large. Is there an explanation? Should we be concerned about this or is it ignorable?
Updated by Olena Kaminska almost 5 years ago
With regard to number 1: you can combine the weights on your own and your thinking is correct. Your weight will be close to ours but imperfect in underrepresenting recent immigrants.
With regard to number 2: thank you for pointing this error to us. We were aware of this and this was corrected for all other weights but for the cross-sectional youth weight for w2. This is now corrected and the updated weight will be released with w7 release. Thanks again.