Score contribution per author:
α: calibrated so average coauthorship-adjusted count equals average raw count
Purchasing power parities (PPPs) are compiled using a two-stage process. In the first stage, prices of items are aggregated without weights to obtain basic heading (BH) PPPs. BH PPPs are then combined using expenditure weights to compute PPPs for major aggregates. This paper derives two results on the reliability of PPPs at the basic heading level.