Something I never understand when defence spending is compared: how do they account for differences in PPP and different levels of grease/corruption? E.g if th

Something I never understand when defence spending is compared: how do they account for differences in PPP and different levels of grease/corruption? E.g if the US spends twice as much as X on fighter planes, but they are built in an uneconomic place because of politics and wages there are double than the average of X. I would say it might mean it actually spends only half, no?