How to avoid 3 common errors in dementia screening

Common error #2: Deviating 
from standardized procedures


While clinicians specifically trained in cognitive measurement are familiar with the rigor by which tests are constructed, those with less training are often unaware that even seemingly minor deviations in procedure can contaminate results as surely as using nonsterile containers in biologic testing, leading to inaccurate interpretations of cognition.

Practical fix: Administer tests 
using verbatim instructions


Failing to follow instructions can significantly bias acquired data, particularly when using performance tests that are timed.

Illustration: Trail Making Test. Trail Making is an old 2-part test developed for the United States Army in the 1940s,¹¹ and used in the Halstead-Reitan neuropsychological battery. Part A is a timed measure of an individual’s ability to join up a series of numbered circles in ascending order. Part B measures the ability to alternately switch between 2 related tasks: namely, alternately joining numbered and lettered circles, in ascending order. This is considered a measure of complex attention, which is often disrupted in early dementia.²⁹

The test uses a specific standardized set of instructions, and Part B’s interpretation depends on having first administered Part A. Anecdotally, we have increasingly seen clinician reports using only Part B. Eliminating Part A removes a significant opportunity for patients to become familiar with the task’s demands, placing them at a considerable disadvantage on Part B and thereby invalidating the normative data.

In addition, follow the exact phrasing of the instructions and use stimuli and response pages that are the same size as those provided in the manual. If a patient errs at any point, it’s important that the test administrator reads, verbatim, the provided correction statements because these statements influence the amount of time spent correcting an error and therefore the final score.

Common error #3: Using 
outdated normative data


Neglecting to use updated norms that reflect current cohort differences can compromise screening accuracy.

Practical fix: Ensure current norms are used for comparisons


Societal influences—computers and other technologies, nutrition, etc—have led to steady improvements in cognitive and physical abilities. In basic psychology, this pattern of improving cognition, documented as an approximate increase of 3 IQ points per decade, is referred to as the Flynn effect.³⁰ Therefore, not only do age and education need to be controlled for, but normative data must be current.

If a patient errs at any point, it’s important that the test administrator reads, verbatim, the provided correction statements.Cognitive screening tools are usually published with norms compiled at the time of the test’s development. However, scores are periodically “re-normed” to reflect current levels of ability. These updated norms are readily available in published journal articles or online. (Current norms for each of the tests used as examples in this article are provided in the references).^21,28,31

Illustration: Trail Making Test. The normative data for this test are not only age- and education-sensitive, but are also highly sensitive to cohort effects. Early norms such as those of Davies,³² while often still quoted in literature and even in some training initiatives, are now seriously outdated and should not be used for interpretation. TABLE 3 shows how an average individual (ie, 50th percentile) in the 1960s, in one of 2 age groups, would compare in speed to an individual of similar age today.³¹ A time score that was at the 50th percentile in 1968 is now at or below the 1st percentile. More recent norms are also usually corrected for education, as are those provided by Tombaugh.³¹

In “A 'case' for using optimal procedures” (below), TABLE 4 shows the results of using outdated Trail Making norms vs current Trail Making norms.