A study of Nassau County Assessment accuracy and fairness

For those who want to delve deeper into Newsday’s study of Nassau County’s 2020-21 tentative assessment roll—and every final roll going back to the 2001-02 tax year—the complete methodology for the prior study it completed for its 2017 “Separate and Unequal” investigation of former County Executive Edward Mangano’s tax system overhaul is contained in the report below this description of the deviations from that approach.

The new study excluded land sales to focus solely on the assessments of homes. It also used the most recent year of available verified sales data leading up to the valuation date for each tax year. For the 2020-21 tax year, this included sales for the year ending July 2018, the most recent data available. The approach is identical to those of a county assessment consultant and state officials who examined the new roll.

For the market condition adjustment only, Newsday used the values of each tax year for its sales-to-assessment ratios with some exceptions for years in which assessment uniformity was poor, the same approach taken with the prior study. For the 2001-02 and 2002-03 tax years, 2003-04 values were used for the sales-to-assessment ratios. For the 2011-12 through 2014-15 tax years, the 2010-11 values were used. And for the 2015-16 to 2019-20 tax years, 2020-21 values were used.

In examining how County Executive Laura Curran’s original and final phase-in plans would have affected accuracy and fairness, Newsday used the final 2019-20 assessment roll as a baseline.

To estimate the first year of the original plan, which called for increasing assessments no more than 6 percent, Newsday increased all assessments by 6 percent, except when the county’s new values were not at least 6 percent higher.

To estimate the first year of the final five-year phase-in plan, Newsday increased the estimated market value of each property by one-fifth of the full increase it would have experienced if not for the phase in.

By Matt Clark

Matt.Clark@newsday.comMattTheJourno

Matt Clark is an investigative reporter, data analyst and computer programmer who has been a member of Newsday's investigative team since 2013. He worked on the 2013 police misconduct series that was a Pulitzer Prize finalist for Public Service.