Interpreter-mediated neuropsychological testing of monolingual Spanish speakers: does it have an effect on test scores?

Nearly 13.8 million Hispanics in the United States speak English "less than very well." This has important implications for the field of clinical neuropsychology. Patients who do not speak English fluently are being increasingly referred for neuropsychological services, and many of these individuals are assessed with the aid of language interpreters. However, whether or how the use of an interpreter has an effect on neuropsychological test scores is not known. For lack of a better alternative, it generally is assumed that the test data obtained through an interpreter are a valid indication of the patient's cognitive functioning, but with almost no empirical support, this assumption appears tenuous at best. The effect of an interpreter, in fact, could be substantial, making this issue all the more deserving of rigorous investigation. The primary objective of the current study was to determine whether using an interpreter to conduct neuropsychological testing of monolingual Spanish speakers had an effect on the neuropsychological test scores. Participants included 40 neurologically normal Spanish-speakers with limited English proficiency, ages 18-65 years, (M= 39.65, SD =13.91) who completed a 2-hour battery of verbal and nonverbal neuropsychological tests both with and without an interpreter. The condition of test administration was counterbalanced across participants and test score differences between the two conditions were compared. Results indicated that use of an interpreter significantly affected mean scores for some neuropsychological tests from the verbal modality. Also, variability in test scores generally was higher when an interpreter was used, significantly so for one verbal test. Results of this study contribute to the extant literature concerning the use of interpreters to facilitate neuropsychological testing of individuals with limited English proficiency. Specifically, they indicate that neuropsychologists should avoid interpreter use and refer patients to bilingual clinicians whenever possible. For situations in which this may not be a viable option, neuropsychologists should limit their test batteries to measures that require minimal reliance on the interpreter. Tests that rely almost entirely on interpreter skills for administration and scoring - such as the Vocabulary and Similarities subtests of the Wechsler Adult Intelligence Scale (WAIS) - should probably not be used. Larger confidence intervals should be used when interpreting observed scores from interpreter-mediated neuropsychological tests.