While the CPI is the price index with the most impact in setting interest rates, the PPI provides significant information earlier in the production process. As a starting point, interest rates have an "inflation premium" and components for risk factors. A lender will want the money paid back from a loan to at least have the same purchasing power as when loaned. The interest rate at a minimum equals the inflation rate to maintain purchasing power and this generally is based on the CPI. Changes in inflation lead to changes in interest rates and, in turn, in equity prices.
The PPI comes in three versions: finished goods; intermediate supplies, materials & components; and crude materials that need further processing. The finished goods PPI is most often cited in the media. This index covers final products bought from producers by businesses to sell to consumers or to use for capital equipment.
The PPI is considered a precursor of both consumer price inflation and profits. If the prices paid to manufacturers increase, businesses are faced with either charging higher prices or they taking a cut in profits. The ability to pass along price increases depends on the strength and competitiveness of the marketplace.