Among cognitively normal elders, our data suggest sex, race, and education level are all associated with performance on an abbreviated version of the BNT. However, the sex differences appear to be secondary to educational disparities among males and females among our older cohort. This difference is not completely surprising, and it likely reflects a generational effect with older males obtaining higher levels of education than older females. Previous research has noted a similar disparity on the 60-item BNT, such that males outperform females in both healthy (Ross & Lichtenberg, 1998
; Welch, Doineau, Johnson, & King, 1996
) and AD samples (Ripich, Petrill, Whitehouse, & Ziol, 1995
). Previous studies have attributed such sex disparities to differing neural networks mediating language among males and females, as females have greater bihemispheric representation for language than males (Vikingstad, George, Johnson, & Cao, 2000
). Superficially, our data corroborate the previous studies, as the elderly NC males outperformed females. However, after further analyses of the data, we found that education may explain the sex differences. Future studies assessing naming performances may wish to include education as a covariate when examining sex differences.
The racial-group differences for BNT-30 performance noted in our study are consistent with some earlier studies, as White elders reportedly obtain higher abbreviated BNT scores than African Americans (Manly et al., 1998
; Manly, Jacobs, Touradji, Small, & Stern, 2002
). These racial disparities have, in part, been explained by educational achievement or literacy differences. For instance, racial discrepancies noted on comprehensive neuropsychological protocols are generally eliminated when educational achievement (Manly et al., 1998
) or a proxy measure of educational quality/literacy (i.e., WRAT-3 Reading subtest) is considered (Manly et al., 2002
). However, it is important to note that previous work has shown that not all racial group differences are attenuated when a proxy measure is considered (Manly et al., 2002
). In contrast to most prior literature, the racial discrepancies noted in the current study remained after the WRAT-3 Reading subtest was included as a covariate. A plausible explanation for the racial disparity is that our chosen proxy measure does not fully encompass the complex set of variables (e.g., socioeconomic factors, cultural experience) that impact educational quality or literacy in this cohort (Manly et al., 2002
). Therefore, researchers and clinicians should exercise caution in relying solely on literacy measures to adjust for racial disparities, as reading level may not fully account for racial differences on some neuropsychological measures.
Older individuals with at least some college education outperformed individuals with a high school education or less. These data are not surprising, as the extant literature contains multiple examples of similar associations between education and performance on the original 60-item BNT (Fox, Warrington, Seiffer, Agnew, & Rossor, 1998
; Welch et al., 1996
). Previous studies have suggested that this education difference may be due to an increase in performance variability among individuals with less than a high school education (Welch et al., 1996
). Our data support this variability theory, as those individuals with less than a high school education had a larger standard deviation for BNT-30 performance as compared to the more educated participants.
The lack of association between age and BNT-30 performance contradicts previous research utilizing the 60-item BNT in a geriatric cohort (Ross & Lichtenberg, 1998
). The discrepancy between our findings and previous research may be secondary to differences in sample demographics, including racial composition and education achievement. More specifically, 81% of our sample is White compared to 44% from a prior study by Ross and Lichtenberg (1998)
. The mean education achievement of our sample was approximately four years greater than that of Ross and Lichtenberg (1998)
. Another explanation for the differences may be that our normative sample was carefully examined to exclude persons with MCI or early symptoms of dementia, which are more common in older samples. Additional research is warranted to clarify an association, if any, between age and naming performance.
The findings from this study augment the extant literature in several ways. First, we present robust normative data for the BNT 30-item even version based on a large sample of healthy controls. Previous studies reporting normative data for abbreviated BNT versions have utilized much smaller sample sizes (Fisher et al., 1999
; Mack et al., 1992
; Williams et al., 1989
), but our normative sample consisted of more than 200 participants. Using this larger sample size, we were able to provide breakdowns according to various demographic variables, including age, education level, education quality/literacy, and race. Furthermore, participants within our sample underwent comprehensive neurodiagnostic work-ups to confirm their normal control status, which increases the likelihood that our normal controls are cognitively and functionally normal.
Despite the numerous strengths of the present study, two limitations must be considered. First, the majority of our sample is comprised of non-Hispanic White individuals (81%); therefore, clinicians using the education or sex breakdown to interpret BNT-30 performance for other racial groups should exercise caution, as our findings suggest there is some racial disparity in BNT-30 performance. Future research should focus on presenting normative data stratified across even larger sample sizes for racial minorities and identifying specific cultural and linguistic variables that may affect performance. Second, our sample underwent a thorough neurodiagnostic evaluation to ensure that participants were normal controls. Therefore, the normative data presented in this study may reflect a “super” geriatric sample rather than something observed in an epidemiological study, which limits the generalizability of our findings.
In summary, the present study compared performances on the BNT 30-item even version among NC, MCI, and AD participants and presented geriatric normative data. Our findings suggest that sex, race, education level, and education quality/literacy are associated with BNT performance; therefore, when interpreting naming performance on this abbreviated measure, normative data or statistical adjustment for these factors should be considered.