Demographically-adjusted norms for the processing speed subtests of the WAIS-III in a Spanish-speaking adult population: Results from the Neuropsychological Norms for the U.S.-Mexico Border Region in Spanish (NP-NUMBRS) project

Abstract

Objective The Wechsler Adult Intelligence Scale (WAIS) processing speed subtests are among the most ubiquitous indices of processing speed in the field. The aim of this study was to develop and examine demographically-adjusted normative data for Spanish language versions of the WAIS-III Digit Symbol Coding (DSC) and Symbol Search (SS) subtests for US-dwelling Spanish-speakers living in the US/Mexico border region. Methods The sample included 203 healthy participants who were part of the larger Neuropsychological Norms for the US-Mexico Border Region in Spanish (NP-NUMBRS) project (DSC: n = 201; SS: n = 200). Results Older age and higher education were both related to lower scores on the DSC and SS subtests (all ps < .0001). There were no significant effects for gender (all ps > .05). Raw-to-scaled score conversions were calculated for both subtests, and fractional polynomial equations were derived to compute demographically-adjusted T-scores accounting for age, education, and gender for each subtest and the Processing Speed Index. Published norms for English-speaking non-Hispanic white adults slightly overestimated impairment rates (T-scores <40) on both the DSC and SS subtests, while the norms for English-speaking non-Hispanic Black/African Americans and the new NP-NUMBRS norms Spanish-speakers both yielded impairment rates that fell within expected limits for healthy controls (i.e. 13%–14%). Conclusions This study suggests that population-specific normative data can improve the diagnostic validity of these measures for U.S.-dwelling Spanish-speakers living in the US/Mexico border region. Future research is needed to investigate the utility of these norms for other U.S.-dwelling Spanish-speaking subpopulations (e.g. Caribbean, Central American, South American).