Derivation
variable: weight (table[s]: this dataset)
variable: ffmass_R (table[s]: this dataset)
variable: dropped_R (table[s]: this dataset)
gen fatmass_R=weight-ffmass_R if ffmass_R~=. & weight~=.
<remove inconsistent data from combined data:>
foreach var in fatmass_R fatmasspc_R ffmass_R ffmasspc_R {
replace `var'=. if dropped_R==1
}