The RAPID-II Neuropsychological Test battery for subjects aged 20 to 49 years: Norms and cognitive profile.

INTRODUCTION: Cognitive evaluation of young subjects is now widely carried out for non-traumatic diseases such as multiple sclerosis, HIV, or sleep disorders. This evaluation requires normative data based on healthy adult samples. However, most clinicians use a set of tests that were normed in an isolated manner from different samples using different cutoff criteria. Thus, the score of an individual may be considered either normal or impaired according to the norms used. It is well established that healthy adults obtained low-test scores when a battery of tests is administered. Thus, the knowledge of low base rates is required so as to minimize false diagnosis of cognitive impairment. The aim of this study was twofold (1) to provide normative data for RAPID-II battery in healthy adults, and (2) estimate the proportion of healthy adults having low scores across this battery.

METHODS: Norms for the 44 test scores of the RAPID-II test battery were developed using the overall sample of 335 individuals based on three categories of age (20 to 29, 30 to 39, and 40 to 49 years) and two educational levels: Baccalaureate or higher educational degree (high educational level), lower than baccalaureate (low educational level). The 5th, 25th, 50th, and 75th percentiles were calculated from the six age and education subsamples and used to define norms. The frequency of low scores on the RAPID-II battery was calculated by simultaneously examining the performance of 33 primary scores. A low score was defined as less than or equal to the 5th percentile drawn from the six age and education normative subsamples. In addition, the percentages of low scores were also determined when all possible combinations of two-test scores across the RAPID-II were considered in the overall normative sample.

RESULTS: Our data showed that 59.4% subjects of the normative sample obtained at least one or more low score. With more than 9 test scores, this percentage was equal to 0% in the normative sample. Among all combinations of two-test scores, 96% had a false positive rate<2%.

CONCLUSION: Low scores are very common in young healthy subjects and are more obvious when simultaneously analyzing test scores across a battery of tests and are thus not necessarily indicative of cognitive impairment. The combinations of two-test scores can be a useful tool to improve the interpretation of low scores.