NIH Public Access Caribbean Black Americans and Non …...Symbol Digit Modalities Test (SDMT) The SMDT is a timed (90s), paper and pencil test. It consists of 1) a key with two rows,

Modified-Symbol Digit Modalities Test for African Americans,Caribbean Black Americans and Non-Latino Whites: NationallyRepresentative Normative Data from the National Survey ofAmerican Life

Hector M. González1, Keith E. Whitfield2, Brady T. West3, David R. Williams4, PeterLichtenberg1, and James S. Jackson5

1 Wayne State University, Institute of Gerontology and the School of Medicine, Department of FamilyMedicine

2 Duke University, Department of Psychology and Neuroscience

3 University of Michigan, Center for Statistical Consultation and Research

4 Harvard School of Public Health, Department of Society, Human Development and Health

5 University of Michigan, Institute of Social Research

AbstractNormative neuropsychological data for U.S. racial/ethnic minorities is limited. Extant norms arebased on small, regional groups that may not be nationally representative. The objectives of this studywere to 1) provide norms for a modified Symbol Digit Modalities Test (M-SDMT) based on anationally representative sample of African Americans, Caribbean Blacks and non-Latino Whites(NLW) living in areas with large populations of Blacks, and 2) determine significant correlates ofM-SDMT performance. The M-SDMT was administered to a subset of respondents from the NationalSurvey of American Life in standard, face-to-face interviews. M-SDMT performance was influencedby race/ethnicity, age, education, and gender. African Americans and NLW groups had similar M-SDMT performances, which differed from Caribbean Blacks. The Black ethnic differences in M-SDMT were not explained by the sociodemographic factors considered in this study. Unlike previouswork, this study supports the consideration of Black ethnicity when evaluating Blackneuropsychological test performance.

KeywordsAfrican Americans; Caribbean Blacks; Blacks; Neuropsychological Tests

INTRODUCTIONA principle objective of the National Institute of Health’s Strategic Plan and Budget to ReduceHealth Disparities is “developing new and improved approaches for detecting, diagnosing,preventing, treating or delaying onset or progression of diseases and disabilities that contributeto health disparities (U.S. DHHS, 2002).” For clinicians and cognitive scientists, it is essentialthat appropriate normative test data be available to screen for cognitive impairment and to

Corresponding Author Hector M. González, Institute of Gerontology, Wayne State University, 87 East Ferry Street, 226 Knapp Building,Detroit, MI 48202, Phone: (313) 577-2297, Fax: (313) 875-0127 Email: [email protected]..

NIH Public AccessAuthor ManuscriptArch Clin Neuropsychol. Author manuscript; available in PMC 2007 December 7.

Published in final edited form as:Arch Clin Neuropsychol. 2007 June ; 22(5): 605–613.

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better understand disease process versus bias artifact in conducting research with diverse andrepresentative U.S. populations (Lampley-Dallas, 2001).

The Symbol Digit Modalities Test (SDMT) is a widely used, brief screening test for neurologicdisorders (Smith, 1968, 1982). The cognitive demands of the SDMT include attention, visualscanning, and motor and psychomotor speed. The SDMT is purportedly sensitive to a wide-range of neurologic and neuropsychiatric disorders, but may lack disorder specificity (Lezak,Howieson, & Loring, 2004). Impaired SDMT performance has been reported in otherwisehealthy adults with white matter hyperintensities, and a variety of pathologic conditions, suchas traumatic brain injury, and subtypes of multiple sclerosis (Felmingham, Baguley, & Green,2004; Huijbregts et al., 2004; Sachdev, Wen, Christensen, & Jorm, 2005). Thus, the SDMT isa useful screening test provided that it is appropriately calibrated to the population of intendeduse.

A recent review of published SDMT normative data indicates that it is widely used; however,normative data is lacking for adult racial/ethnic minority groups (Sheridan et al., 2005). Inrecent years, more normative data for African Americans have become available forneuropsychological tests (e.g., (Byrd, Touradji, Tang, & Manly, 2004; Moering, Schinka,Mortimer, & Graves, 2004). Most studies have focused on adults over age 60, which may beof limited utility to clinicians and investigators working with a wider range of adults(Fillenbaum, Heyman, Huber, Ganguli, & Unverzagt, 2001; Friedman, Schinka, Mortimer, &Graves, 2002; Lucas et al., 2005; Manly, Byrd, Touradji, & Stern, 2004; Mast, Fitzgerald,Steinberg, MacNeill, & Lichtenberg, 2001). Additionally, ethnicity among Blacks and testperformance has rarely been examined (Byrd, Sanchez, & Manly, 2005). Currently, normativedata is unavailable for younger Caribbean Blacks who, some argue, may be culturally andsocioeconomically distinct from other Blacks (Williams & Jackson, 2000). The purposes ofthis study were to determine significant correlates of a modified version of the SDMTperformance and provide normative data for clinical and research use from a large, nationallyrepresentative sample of African Americans, Blacks of Caribbean ancestry, and non-LatinoWhites (NLW) living in areas with large populations of Blacks.

METHODSParticipants

Participants in this study were from the National Survey of American Life (NSAL), which isa population-based, multi-stage probability sample of 6,082 African American, CaribbeanBlacks, and non-Latino White (NLW), ages 18–94) residing in the U.S. The NSAL, along withthe National Comorbidity Survey Replication (NCS-R) and the National Latino and AsianAmerican Study (NLAAS), is a part of the Collaborative Psychiatric Epidemiology Surveys.Details of the sampling methodology and sampling weight calculations for the NSAL havebeen previously published (Heeringa et al., 2004).

The NSAL adult sample was an integrated national household probability sample of 3,570African Americans, 891 NLW, and 1,621 Blacks of Caribbean descent (Caribbean Blacks),for a total sample of 6,082 individuals aged 18 and over. The core African American sampleis a nationally representative sample of households located in the 48 coterminous states withat least one Black adult 18 years or over who did not identify ancestral ties in the Caribbean.The Caribbean Black sample was selected from two area probability sample frames (i.e., 265came from the households in the core sample frame, while 1,356 came from an area probabilitysample of housing units from geographic areas with a relatively high density of persons ofCaribbean descent). The NSAL analysis weights for the African American and CaribbeanBlack samples were designed to provide population representation for these populations in the48 coterminous states. Caribbean Blacks included persons who self-identified as Black, and

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answered affirmatively when asked if they 1) were of West Indian or Caribbean descent, or 2)indicated that they were from a country included on a list of Caribbean area countries presentedby the interviewers, or 3) indicated that their parents or grandparents were born in a Caribbeanarea country. The NLW sample was a stratified, disproportionate sample of NLW adultsresiding in households located in Census 2000 tracts and blocks that have 10% or greaterAfrican American populations. The sample design and sample analysis weights weredetermined so that they would be optimal for comparative analyses in which residential,environmental, and socioeconomic characteristics were controlled for in Black-NLW statisticalcontrasts.

The interviews used in this study were conducted face-to-face using interviews that averagedtwo hours and twenty minutes in length. Data collection was conducted between February 2001and June 2003. The overall response rate was 72.3% and varied by race and ethnicity: 70.7%for African Americans; 77.7% for Caribbean Blacks; and 69.7% for the NLW. Additionalinformation on the NSAL data collection has been previously published (Pennell et al.,2004).

Sample respondents were included in this study if they had completed at least one section ofthe cognitive test and did not meet criteria for any of the following Diagnostic and StatisticalManual (DSM) IV psychiatric conditions in the past twelve months: 1) panic disorder; 2)agoraphobia without panic disorder; 3) social phobia; 4) generalized anxiety disorder; 5) majordepression; 6) dysthymia; and 7) bipolar I or II (APA, 1994). The DSM-IV, World MentalHealth Composite Interview (WHO CIDI), which is a fully structured diagnostic interview,was used to assess the mental disorders itemized above. Of the 6,082 respondents in the NSALsample, 4,545 (74.73%) were included in the study per the criteria above, 712 (11.71%) hadat least one condition, and the remaining 825 (13.56%) did not have information collected onthe disorder or SDMT measures due to incomplete data, physical impairment and refusals.Commands appropriate for subpopulation analyses of survey data in SAS Version 9.1.3 (SASInstitute, Inc., Cary, NC) and Stata Release 9 (StataCorp LP, College Station, TX) softwarewere utilized when analyzing the data collected for this subpopulation.

Symbol Digit Modalities Test (SDMT)The SMDT is a timed (90s), paper and pencil test. It consists of 1) a key with two rows, withnine stimulus symbols in the upper row, and matched numbers (1–9) in the lower row, and 2)a two-row grid with the same nine stimulus symbols in the upper row and blank cells fornumeric responses in the lower row (Smith, 1982). This modified version of the SDMT, calledthe Modified Symbol Digit Modalities Test (M-SDMT) has 50 response cells and two parts(A and B). Parts A and B use the same stimulus and numeric coding system. The M-SDMThas been previously used in a study of genetics among African Americans twins (Whitfield,Brandon, Wiggins, Vogler, & McClearn, 2003); however, detailed characteristics of the M-SDMT have not been previously published. The examinee is given 45s to complete each part(A and B). All tests were administered to NSAL respondents in the paper and pencil format.

ScoringThere are three separate scores for the M-SDMT. They are 1) the total number of correctresponses for Part A (out of 50 possible); 2) the total correct responses for Part B (out of 50);and 3) the total correct responses for Parts A and B combined (total possible was 100).

Statistical AnalysisAll statistical analyses performed in the study were design-based, taking the NSAL samplingweights into account to ensure that estimates were representative of the respective ethnicpopulations in the U.S., and using the NSAL sample design variables to calculate standard



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errors for statistical estimates appropriately reflecting the stratified, clustered design of theNSAL sample. Analyses were performed using procedures for design-based analysis of surveydata in SAS Version 9.1.3 (SAS Institute, Inc., Cary, NC) and Stata Release 9 (StataCorp LP,College Station, TX).

Descriptive analyses of the survey data were performed to generate tables of normative datafor the scores on the M-SDMT, indicating weighted estimates of means, weighted estimatesof standard deviations, and sample sizes for cross-classifications of the NSAL populationdefined by gender, ethnicity, age, and education. The relationships between SDMTperformance and demographic variables were also evaluated in the analyses. Linear regressionmodels were used to model the three dependent variables representing the three M-SDMTscores. Independent variables included ethnicity (African Americans, Caribbean Blacks andNLW) and gender as categorical factors, in addition to age and education as continuousindependent variables. Terms to model the interaction of ethnicity with other independentvariables were also included in the models. Thus, the following independent variables wereincluded in the models: ethnicity, education, gender, age, ethnicity × age, ethnicity × education,and ethnicity × gender. Values for the age and education variables were mean-centered bysubtracting from each variable the overall mean for the subpopulation of interest meeting theinclusion criteria, to avoid problems associated with collinearity of interaction terms and maineffects (Rawlings, Pantula, & Dickey, 1998). Standard diagnostic tests were used to assess theappropriateness of all assumptions behind the linear regression models (e.g., normality andconstant variance for the random errors).

RESULTSDemographic Characteristics of Groups

The demographic characteristics of the NSAL subsample meeting the inclusion criteria for thisstudy are presented in Table 1. Consistent with 2000 U.S. Census data, the African Americanand Caribbean Black samples were younger, more likely to be female, and had fewer years ofeducation than the NLW sample (Census, 2000). Overall, ages ranged from 18 to 94 yearsacross the three groups.

Regression ModelsTable 2 presents regression models indicating the estimated relationships of age, education andgender to the dependent variables measuring scores on Parts A, B and the Total (Part A + PartB) of the M-SDMT. In each of the three models (not shown), none of the two-way interactionsbetween the demographic variables and ethnicity were found to be significant (p<.05), basedon design-adjusted Wald tests for the interaction effects. The results of these models indicatethat there are significant main effects of these demographic variables on the scores, and thatthe effects do not vary for different subgroups. Age was found to have a significant negativerelationship with each of the three scores, education was found to have a positive relationshipwith each of the three scores, and females were found to have significantly higher means oneach score than males. In addition, Caribbean Blacks were found to have a significantly lowermean than both African Americans and NLW on each of the three scores. These main effectsare evident in the weighted means and standard deviations presented in Tables 3 through 5.

Normative SDMT DataTables stratified by ethnicity, age, education and gender are presented for M-SDMT Part A(Table 3), Part B (Table 4) and the Total Score (Table 5), with weighted estimates of meansand standard deviations based on the NSAL subsample. The respective cell sample sizes usedto compute the table estimates are provided as well.



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DISCUSSIONThe M-SDMT was developed to improve detection and aid in the diagnosis of disorders forprevention, treating and delaying onset or progression of diseases and disabilities in differentethnic/racial groups. The normative data presented here for the M-SDMT are based on thelargest sample of U.S. Blacks ever published. In addition, due to the extensive samplingprocedures, the data are highly representative of U.S. Blacks and geographically similar NLW.Further, statistical corrections for significant predictors of M-SDMT performance shouldfurther assist the user in controlling demographic biases. The relationships of the demographicpredictors with M-SDMT performance reported in this study were found in additional analyses(not reported) to be similar and significant in each of the three ethnic subgroups. This suggeststhat demographic differences between the groups were not attenuating the relationships ofimportant demographic predictors with M-SDMT performance, and that the demographicpredictors considered should be controlled for when predicting performance. While the resultsof this study should be generalizable to African Americans and Caribbean Blacks in the U.S.,it is important for users of the M-SDMT to be cognizant of limited generalizability of the M-SDMT to all NLW because the sample in this study is a unique group that may differ from themajority of NLW. The normative data in this report for the M-SDMT should provide cliniciansand researchers with appropriate information for using this screening test with AfricanAmerican, Caribbean Blacks and NLW from areas with larger concentrations of Blacks.

In this study, African American and NLW groups did not differ significantly on M-SDMTperformance; however, the Caribbean Black group had significantly lower performancescompared to the African American and NLW groups. The findings of this study are consistentwith previous work with older adults that ethnic differences among Black Americans shouldbe considered when evaluating cognitive performance using tests like the M-SDMT (Byrd,Sanchez, & Manly, 2005). It is not clear from the results of this study if otherneuropsychological tests would be similarly affected by Black ethnicity.

The M-SDMT performance differences between Black ethnicity groups were likely to havebeen associated with factors other than the demographic variables considered in this study. Thedemographic variables examined in this study explained a small fraction (16.2%) of thepossible total variance associated with M-SDMT performance. This suggests that other factorscould explain the ethnic differences in M-SDMT. Reading performance has been previouslyshown to predict cognitive test performance among African Americans and Caribbean Blacks(Byrd, Sanchez, & Manly, 2005; Manly, Byrd, Touradji, & Stern, 2004); however, readinglevel was not examined in the NSAL. In previous work with Latinos, associations betweennativity, acculturation, and cognitive function were found (González et al., unpublishedmanuscript). The influences of nativity and acculturation have only recently been examinedamong Blacks. Previous work with the NSAL Caribbean Black sample has shown thatpsychopathology varies by U.S. acculturation (Williams et al., 2007). It is possible that thelevel of acculturation within the Caribbean Black sample may have contributed to the ethnicdifferences observed in this study. This study did not consider the associations between M-SDMT performance and indicators of acculturation, such as nativity and years of U.S.residency. Although previous work has found trends between acculturation and cognitiveperformance among older Caribbean Blacks (Byrd, Sanchez, & Manly, 2005; Manly, Byrd,Touradji, & Stern, 2004), these associations merit further investigation in future studies withlarger and younger adult samples (Whitfield, 1998a, 1998b).

In summary, the M-SDMT is a brief screening test, and the normative data presented in thisstudy should prove useful to clinicians and researchers interested in assessing the cognitivefunctioning of African American and Caribbean Blacks and NLW living in areas with larger



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Black populations. Further examinations of the between and within group variability areneeded to better explain the similarities and differences between these ethnic/racial groups.

Acknowledgements

The research was supported by grants from the National Institute of Mental Health (MH 67726, H.M. González; MH57716, J. Jackson). The authors would like to express our thanks to Myriam Torres and Julie Sweetman for editingthis manuscript.

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Psychiatric Association; 1994.Byrd DA, Sanchez D, Manly JJ. Neuropsychological test performance among Caribbean-born and U.S.-

born African American elderly: the role of age, education and reading level. J Clin Exp Neuropsychol2005;27(8):1056–1069. [PubMed: 16207624]

Census, U. American FactFinder. 2000. from http://www.census.gov/Heeringa SG, Wagner J, Torres M, Duan N, Adams T, Berglund P. Sample designs and sampling methods

for the Collaborative Psychiatric Epidemiology Studies (CPES). Int J Methods Psychiatr Res 2004;13(4):221–240. [PubMed: 15719530]

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Lezak, M.; Howieson, DB.; Loring, DW. Neuropsychological Assessment. New York: Oxford UniversityPress; 2004.

Manly JJ, Byrd DA, Touradji P, Stern Y. Acculturation, reading level, and neuropsychological testperformance among African American elders. Appl Neuropsychol 2004;11(1):37–46. [PubMed:15471745]

Pennell BE, Bowers A, Carr D, Chardoul S, Cheung GQ, Dinkelmann K, et al. The development andimplementation of the National Comorbidity Survey Replication, the National Survey of AmericanLife, and the National Latino and Asian American Survey. Int J Methods Psychiatr Res 2004;13(4):241–269. [PubMed: 15719531]

Rawlings, JO.; Pantula, SG.; Dickey, DA. Applied regression analysis: a research tool. 2. New York:Springer; 1998.

Sheridan LK, Fitzgerald HE, Adams KM, Nigg JT, Martel MM, Puttler LI, et al. Normative Symbol DigitModalities Test performance in a community-based sample. Arch Clin Neuropsychol. 2005

Smith, A. The symbol-digit modalites test: a neuropsychologic test of learning and other cerebraldisorders. In: Helmuth, J., editor. Learning Disorders. Seattle: Special Child Publications; 1968. p.83-91.

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US DHHS, N. I. o. H.. Strategic Research Plan and Budget to Reduce and Ultimately Eliminate HealthDisparities Volume I. 2002.

Whitfield KE. Conceptual Issues and Analytic Strategies for Studying Cognition in Older AfricanAmericans. African-American Research Perspectives 1998a;4(1):115–125.

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Table 2Nationally Representative Estimates of Modified-Symbol Digit Modalities Test Performance by AfricanAmerican, Caribbean Blacks and Non-Latino Whites living in areas with large Black populations. Samples fromthe National Survey of American Life.Reported are Estimated Multiple Regression Models Predictors of (Design-based Parameter Estimates and Standard Errors).

Total Part A Total Part B Total (Part A + Part B)

Constant 20.736 (0.391)** 22.246 (0.383)** 42.991 (0.748)** Age (Centered) −0.201 (0.015)** −0.188 (0.016)** −0.387 (0.032)** Education (Centered) 0.658 (0.114)** 0.773 (0.109)** 1.418 (0.212)** Female 1.084 (0.349)** 0.883 (0.377)* 2.017 (0.678)**Ethnic Group African American REF REF REF Caribbean Black −2.202 (0.671)** −1.758 (0.649)** −3.960 (1.178)** Non-Latino White 0.486 (0.792) 0.769 (0.970) 1.371 (1.730)

*p < 0.05

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Table 3Normative Data for a Part A of the Modified-Symbol Digit Modalities Test based on Estimates from a NationallyRepresentative African American, Caribbean Blacks and Non-Latino Whites from Areas with Large Populationsof Blacks.


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Table 4Normative Data for a Part B of the Modified-Symbol Digit Modalities Test based on Estimates from a NationallyRepresentative African American, Caribbean Blacks and Non-Latino Whites Living in Areas with LargePopulations of Blacks.


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Table 5Normative Data for a Parts A and B of the Modified-Symbol Digit Modalities Test based on Estimates from aNationally Representative African American, Caribbean Blacks and Non-Latino Whites Living in Areas withLarge Populations of Blacks.


Documents

NIH Public Access Caribbean Black Americans and Non …...Symbol Digit Modalities Test (SDMT) The SMDT is a timed (90s), paper and pencil test. It consists of 1) a key with two rows,