Derivation
variable: ident (table[s]: gen_spouse)
variable: idspouse (table[s]: gen_spouse)
variable: idmoth (table[s]: gen_identity)
variable: idfath (table[s]: gen_identity)
gen incest=0
replace incest=1 if (ident_idmoth==idspouse & ident_idmoth~="" & idspouse~="") | (ident_idfath==idspouse & ident_idfath~="" & idspouse~="") | (idspouse_idmoth==ident & idspouse_idmoth~="" & ident~="") | (idspouse_idfath==ident & idspouse_idfath~="" & ident~="")