Derivation
variable: biovalf (table[s]: arkk_arkq, arkl_arkq, kduk_kduq, kdul_kduq)
variable: biovals (table[s]: arkk_arkq, arkl_arkq, kduk_kduq, kdul_kduq)
variable: imp_final (table[s]: gap_combined)
<ARK & KDU data:>
egen impval=rowmean(biovalf biovals)
<NUT data:>
egen impval=rowmean(imp_ohms_bs imp_ohms_bs_2)