This dataset is a county-by-county list of the estimated reduction in house values in about 3,000 counties throughout the country, as calculated by Mark Zandi, the chief economist of Moody’s Analytics. ProPublica used this data in "Trump’s Trillion-Dollar Hit to Homeowners," which highlighted its findings and identified the five counties with the largest estimated reductions: Essex County, New Jersey; Westchester County, New York, suburban New York City; Union County, New Jersey, which is adjacent to Essex County; New York County, the New York City borough of Manhattan; and Lake County, Illinois, suburban Chicago.
This dataset includes two columns — the county and the estimated percent reduction. To calculate the estimated reduction, Zandi took what financial analysts call the present value of the property tax and mortgage interest deductions that homeowners will lose over seven years (the average duration of a mortgage) because of changes in the tax law and subtracted it from the value of the typical house. That calculates the reduction in each county’s home values below what they would otherwise be. Zandi then adds an additional one percentage point of value shrinkage, which comes from the higher interest rates that he says will result from the higher federal budget deficits caused by the tax bill. He estimates that rates on 10-year Treasury notes, a key benchmark for mortgage rates, will be 0.2% higher than they would otherwise be, which in turn will make mortgage rates 0.2% higher.