; and (bb) that is related to the prevalence of non-fatal drug overdoses, drug overdose deaths, and the mortality rate from drug overdoses and provides an equivalent measure of need for funding. (iii) Number of drug overdose deaths The number of drug overdose deaths determined under this clause for an eligible county for a fiscal year for purposes of clause (ii) is the number of drug overdose deaths during the most recent 3-year period for which such data are available. (iv) Number of non-fatal drug overdoses The number of non-fatal drug overdose deaths determined under this clause for an eligible county for a fiscal year for purposes of clause (ii) may be determined by using data including emergency department syndromic data, visits, or other emergency medical services for drug-related causes during the most recent 3-year period for which such data are available. (v) Study Not later than 3 years after the date of enactment of this title, the Comptroller General shall conduct a study to determine whether the data utilized for purposes of clause (ii) provide the most precise measure of local area need related to substance use and addiction prevalence in local areas and whether additional data would provide more precise measures of substance use and addiction prevalence in local areas. Such study shall identify barriers to collecting or analyzing such data, and make recommendations for revising the distribution factors used under such clause to determine funding levels in order to direct funds to the local areas in most need of funding to provide substance use disorder treatment services. (vi) Reductions in amounts If a local area that is an eligible local area for a year loses such eligibility in a subsequent year based on the failure to meet the requirements of section 3401(b)(1)(A), such area will remain eligible to receive— (I) for such subsequent year, an amount equal to 80 percent of the amount received under the grant in the previous year