Correlation Between the Bilingual Status and the Onset Age of AD and MCI Subjects: Evidence from the ADNI Dataset

Abstract

Background: This paper investigates the statistical relationship between bilingualism and the Onset Age (OA) of AD and MCI across a clinical sample, consisting of 580 Alzheimer's Disease (AD) subjects and 1264 Mild Cognitive Impairment (MCI) subjects, via a statistical analysis conducted on the sample retrieved from the Alzheimer's Disease Neuroimaging Initiative (ADNI) dataset. Method: To investigate whether bilingualism has any correlation with the OAs of AD or MCI subjects, our study leverages the full potential of the ADNI dataset, a dataset that covers both the OA and the bilingualism status of both the AD and MCI subjects. Prior to performing any meaningful statistical analysis, a regression model and a probabilistic model were developed in parallel to fill in the missing OA and bilingualism values. A simple least-square regression model that consists of an independent variable of registered age for Mini-Mental State Examination (MMSE) score was used to estimate the OA of the AD and MCI subjects in the ADNI dataset. After filling in the missing OA values, the number of subjects relevant for the statistical analysis increased from 816 (AD: 371, MCI: 445) to 1844 (AD: 580, MCI: 1264), which greatly enlarged the representation of the AD and MCI sample in the ADNI population. With increased sample size, a novel probabilistic classification model was introduced to infer an ADNI subject’s bilingualism when relevant demographic information and deterministic outcome were not readily available from the ADNI dataset. The weighted average OA for the bilinguals and the monolinguals was then computed, where the weights for the probabilistic labels were assigned based on the percentage of bilingualism in the general US population. Finally, a statistical analysis was performed to test whether any statistically significant correlation exists between the OA and the bilingualism of the AD and MCI subjects within the ADNI dataset. Findings: Our preliminary study demonstrates no significant statistical difference between the OA of the bilinguals and the monolinguals within the ADNI dataset. Thus, the monolingual speakers within the ADNI dataset do not statistically manifest earlier onset, as compared to the bilingual speakers, which is slightly inconsistent with some earlier statistical findings that bilingual speakers enjoy certain distinctive advantages, such as late onset of AD, as compared to monolingual counterparts.