PPP comparisons are useless. You can't adjust the price of international inputs- imported machinery or a ticket from San Francisco to Beijing, particularly in an export-oriented economy, the utility of PPP comparisons is virtually nil. The Chinese economy remains about half the size of the American.
Imports are never counted anyway in GDP- they subtract from it. And internationally traded goods are not price-adjusted for PPP calculations anyhow. That's a common mistake people make when critiquing PPP adjustments. Price index deviations are solely result of weighted non-tradable goods surveyed at different prices.
