Brief Test of Attention: Normative data for the Latin American Spanish speaking adult population

2.1Participants

The sample consisted of 3,977 healthy individuals who were recruited from Argentina, Bolivia, Chile, Cuba, El Salvador, Guatemala, Honduras, Mexico, Paraguay, Peru, and, Puerto Rico. The participants were selected according to the following criteria: a) were between 18 to 95 years of age, b) were born and currently lived in the country where the protocol was conducted, c) spoke Spanish as their native language, d) had completed at least one year of formal education, e) were able to read and write at the time of evaluation, f) scored ≥23 on the Mini-Mental State Examination (MMSE, Folstein, Folstein, & McHugh, 1975), g) scored ≤4 on the Patient Health Questionnaire–9 (PHQ-9, Kroenke, Spitzer, & Williams, 2001), and h) scored ≥90 on the Barthel Index (Mahoney & Barthel, 1965).

Participants with self-reported neurologic or psychiatric disorders were excluded due to a potential effect on cognitive performance. Participants were volunteers from the community and signed an informed consent. Seven participants were excluded from the analyses, with a final sample of 3,970 participants. Socio-demographic and participant characteristics for each of the countries’ samples have been reported elsewhere (Guàrdia-Olmos, Peró-Cebollero, Rivera, & Arango-Lasprilla, 2015). The multi-center study was approved by the Ethics Committee of the coordinating site, the University of Deusto, Spain.

2.2Instrument administration

The BTA test consists of two equivalent forms that are administered consecutively (Forms N and L). In the N form, the subject hears a list of 10 series of letters and numbers that are intercalated (for example: “5 –K –7 –H”), after which the subject must indicate how many numbers were mentioned. The series of letters and numbers increase in length, from 4 to 18 items (Schretlen, et al., 1996a; Spreen & Strauss, 1998). Subsequently, in the form L, the subjects are presented the same list series, but this time the subject must indicate how many letters were mentioned (Schretlen et al., 1996a). The test is done while the subject holds his or her hands and keeps them in view of the examiner, in this way the subject is unable to count with fingers (Spreen & Strauss, 1998). The total score of each form is equal to the number of correct answers, and the total score is the sum of the scores in the forms N and L (Schretlen et al., 1996a).

2.3Statistical analyses

The detailed statistical analyses used to generate the normative data for this test are described in Guàrdia-Olmos, et al. 2015. In summary, the data manipulation process for each country-specific dataset involved five steps: a) t –tests for independent samples and effect sizes (r) were conducted to determine gender effects. If the effect size was larger than 0.3, gender was included in the model with gender dummy coded and female as the reference group (male = 1 and female = 0). b) A multivariable regression model was used to specify the predictive model including gender (if effect size was larger than 0.3), age as a continuous variable, and education as a dummy coded variable with 1 if the participant had >  12 years of education and 0 if the participant had 1–12 years of education. If gender, age and/or education was not statistically significant in this multivariate model with an alpha of 0.05, the non-significant variables were removed, and the model was re-run. Then a final regression model was conducted that included age (if statistically significant in the multivariable model), dichotomized education (if statistically significant in the multivariate model), and/or gender (if effect size was greater than 0.3) [yˆi=βo+(βAge·Agei)+(βEduc·Educi)+(βGender·Genderi)]; c) residual scores were calculated based on this final model (ei=yi-yˆi); d) using the SD (residual) value provided by the regression model, residuals were standardized: z = e _i /SD _e , with SD _e (residual) = the standard deviation of the residuals in the normative sample; and e) standardized residuals were converted to percentile values (Strauss et al., 2006). Using each country’s dataset, these steps were applied to BTA scores.

3.1Normative procedure

Norms (e.g., a percentile score) for the BTA scores were established using the five-step procedure described above. To facilitate the understanding of the procedure to obtain the percentile associated with a score on this test, an example will be given. Suppose you need to find the percentile score for a Bolivian woman, who is 60 years old and has 7 years of education. She has a score of 12 on the BTA. The steps to obtain the percentile for this score are: a) Check Table 1 to determine if the effect size of gender in the country of interest (Bolivia) on this test and time point (BTA) is greater than 0.3 by country. The column labeled r in Table 1 indicates the effect size. In this example, the effect size is 0.078, which is not greater than 0.3. For Bolivian on this test, gender does not influence scores to a sufficient degree to take it into account gender when determining the percentile. b) Find Bolivia in Table 2, which provides the final regression models by country for BTA. Use the B weights to create an equation that will allow you to obtain the predicted BTA score. The corresponding B weights are multiplied by the actual age and dichotomized education scores and added to a constant in order to calculate the predicted value. In this case, the predicted BTA score would be calculated using the equation [yˆi=14.942+(-0.059·Agei)+(1.943·DichotomizedEducationalLeveli)] (the values have been rounded for presentation in the formula). The subscript notation i indicates the person of interest. The person’s age is 60, but the education variable is not continuous in the model. Years of education is split into either 1 to 12 years (and assigned a 0) or more than 12 years (and assigned a 1) in the model. Since our hypothetical person in the example has 7 years of education, her educational level value is 0. Thus the predicted value is yˆi=14.942+(-0.059·60)+(1.943·0)=14.942-3.517+0=11.424. c) In order to calculate the residual value (indicated with an e in the equation), we subtract the actual value from the predicted value we just calculated (ei=yi-yˆi). In this case, it would be e _i  = 12 - 11.42 = 0.576. d) Next, consult the SD _e column in Table 2 to obtain the country-specific SD _e (residual) value. For Bolivia, it is 3.786. Using this value, we can transform the residual value to a standardized z score using the equation (e _i /SD _e ). In this case, we have 0.576/3.786 = 0.152 . This is the standardized z score for a Bolivian woman aged 60 and 7 years of education and a score of 12 on the BNT. e) The last step is to use look up the tables in the statistical reference books (e.g. Strauss et al., 2006) or use a trusted online calculator like the one available at http://www.measuringu.com/pcalcz.php. In the online calculator, you would enter the z score and choose a one-sided test and note the percent of area after hitting the submit button. In this case, the probability of 0.152 corresponds to the 56thpercentile.

3.2User-friendly normative data Tables

The five-step normative procedures explained above can provide more individualized norms. However, this method can be prone to human error due to the number of required computations. To enhance user-friendliness, the authors have completed these steps for a range of raw scores based on small age range groupings (see Guàrdia-Olmos, et al., 2015) and created tables so that clinicians can more easily use to obtain a percentile range associated with a given raw score on this test. These tables are available by country and type of test (BTA) in the Appendix. In order to obtain an approximate percentile for the above example (converting a raw score of 12 for a Bolivian women who is 60 years old and has 7 years of education) using the simplified normative tables provided, the following steps are recommended. (1) First, identify the appropriate table ensuring the specific country and test. In this case, the table for BTA scores for Bolivia can be found in Table A2. (2) Note if the title of the table indicates that it is only to be used for one specific gender. In this case, gender is not specified. Thus Table A2 is used for both males and females. (3) Next, the table is divided based on educational level (1 to 12 vs. more than 12 years of education). Since this woman has 7 years of education, she falls into the “1 to 12 years of education” category. These data can be found in the low section of the table. (4) Determine the age range most appropriate for the individual. In this case, 60 fall into the column 58–62 years of age. (5) Read down the age range column to find the approximate location of the raw score the person obtained on the test. Reading down the 58–62 column, the score of 12 obtained by this Bolivian woman corresponds to an approximate percentile of 60.

The percentile obtained via this user-friendly table method (60th) is slightly different than the more exact one (56th) obtained following the individual conversion steps above because the table method is based on an age range (e.g., individuals aged 58–62) instead of the exact age (individuals aged 60). If the exact score is not listed in the column, you must estimate the percentile value from the listed raw scores.

4.1Limitations and future directions

This study has several limitations, and as a result directions for future research. First, this study was subject to a number of sampling limitations. First, although the BTA is an extremely common neuropsychological measure in Latin America, many other common assessments need to be normed in the same manner as the current study. Future research should examine the psychometrics of other common instruments in Latin America. Research should also examine the ecological validity of various neuropsychological assessments in this region, and if not, create instruments in those cultures that have better ecological validity. Indeed, the BTA has been shown to have good sensitivity in predicting activities of daily living among adults with severe mental disorders (Schretlen et al., 1997), but nonetheless the BTA was created in a Western culture that may differ from those in Latin America. Future research should develop culturally sensitive assessments within local cultures, not just translate and norm tests from other cultures and countries as occurred in the current study.

Second, participants all spoke Spanish as their primary language, but BTA performance could be different among people who speak various secondary languages. An important area for future research is bilingualism and performance on the BTA which was not assessed in the current study. Also, the data were collected in specific regions of the countries in the current study, not nationally. This study represents the largest neuropsychological normative study in the history of Latin America for the BTA, as well as in any global region, but it is only a first step in for larger studies with nationally representative samples. Many participants had fewer than 12 years of education, but those unable to read or write were excluded. As a result, the norms from the current study are limited in their ability to generalize to illiterate adults. Similarly, participants in the current study were excluded if they had a history of neurological conditions, so future studies should include neurological populations, as well as children.

Third, clinicians exercise caution in applying the BTA norms from this study to individuals in countries beyond the 11 countries from which data were collected. Future studies should establish BTA norms in other Latin American countries including as Ecuador, Uruguay, Venezuela, and Panama. However, these BTA norms may be more accurate in those countries than other norms currently in use. This generalizability is a critical area for future research.

Despite these limitations and because no Spanish norms have yet been established for the BTA, this study was the first to generate BTA norms across 11 countries in Latin America with nearly 4,000 participants. As a result, this was the largest and most comprehensive BTA normative study conducted in any global region, and its norms will likely affect the standard of neuropsychological assessment with the BTA in Latin America unlike any study before it.