Investigating the relationship between dementia and cognitive tests performance : do better scores on cognitive tests relate to a lower risk of developing dementia?

Sammanfattning: In 2021, dementia was the seventh leading cause of death among all diseases in the world according to the World Health Organization (2021). Dementia is an overall medical term indicating deteriorated brain health associated with loss of memory, cognitive abnormality and difficulties in daily activities. There is no medical cure for dementia yet. However, if we can detect early brain changes through various cognitive tests, we may delay the progression of dementia. The purpose of this study is to investigate the relationship between dementia and cognitive tests. We use two methods to examine their relationship. The first method is called an extended Cox model. Since we are using longitudinal data regarding cognitive aging provided from the Betula Project collected from 1988 to 2010 with repeated cognitive examinations from four different sample groups, we introduce time-varying covariates in the usual Cox proportional hazard model. Secondly, the regularization method from the extended Cox model is implied. We have 12 cognitive tests and four additional covariates such as genetic information (APOEe4), information on age, sex and education to fit into the extended Cox model. As a result, we have many variables in the regression. If we can shrink the model, we can examine which variables have more important relations to dementia. With an aim to find more important variables, we apply the Elastic net regularization. To sum up, an extended Cox regression and a regularized extended Cox model are fitted to investigate the relationship between dementia and cognitive test results. The study finds that a person who performs better at Episodic Memory test, Prospective Memory test and/or Mini-Mental State Examination, has lower risk of developing dementia.