Understanding Society User Support

Dear staff from Understanding Society,

I am currently doing a research which requires to link the parents and children's birthday. I mainly use the two data file "xwavedat_protect", "xwaveid_bh_protect" (although I don't know what's the difference between two datasets) and also "xhhrel_protect". Based on previous issues, I tried to follow your "do file" by firstly rename the pidp. My code is like:

using "xwavedat_protect"

gen bcx_pidp_1 = pidp //bcx_pidp_1 means the first biological child

save "xwavedat_protect", replace

using "xhhrel_protect"

merge 1:m bcx_pidp_1 using "xwavedat_protect"

Then it shows errors, variable bcx_pidp_1 does not uniquely identify observations in the master data

I would be really appreciate if you could help me solve this issue.