These areas have the highest Home Price Index according to FHFA. The FHFA House Price Index (FHFA HPI) is a broad measure of the movement of single-family house prices in the United States. The HPI is a weighted, repeat-sales index, meaning that it measures average price changes in repeat sales or refinancings on the same properties. This information is obtained by reviewing repeat mortgage transactions on single-family properties whose mortgages have been purchased or securitized by Fannie Mae or Freddie Mac. The index is based on a score of 100 in the year 2000. A score of 200 would indicate that house prices have doubled since 2000.