Cognitive testing for dementia has a problem in that low scores on some tests may simply reflect a person's weakness in some cognitive areas, or the presence of a relatively benign form of mild cognitive impairment (one that is not going to progress to dementia). A 2008 study found that one of every six healthy adults scored poorly on two or more of 10 tests in a brief cognitive battery. Following this up, the same researchers now show that a more holistic view might separate those who are on the path to dementia from those who are not.

Data from 395 clinical patients (aged 60+) and 135 healthy older adults has revealed that, while the cognitively normal produce a pattern of scores on 13 cognitive tests that fits a bell-shaped curve, those experiencing some level of dementia produce a more skewed pattern. Increasingly lower scores and degree of positive skew was also associated with worsening dementia.

http://www.futurity.org/lopsided-cognition-may-predict-early-alzheimers/

http://www.eurekalert.org/pub_releases/2013-11/jhm-jhr111113.php

[3601] Reckess, G. Z., Varvaris M., Gordon B., & Schretlen D. J.
(2014).  Within-person distributions of neuropsychological test scores as a function of dementia severity.
Neuropsychology. 28(2), 254 - 260.