Drawing a Clock Is a Useful Cognitive Tool — But It Has Its Limits

Drawing a clock face has become a ubiquitous way to measure your brain’s health – whether you’re assessing dementia, encephalitis or the presence of a traumatic brain injury. It’s even shown up as a plot point on the TV show Hannibal. Spend enough time reading about the clock test and you’ll see some sharply contrasting images: a healthy person drawing a clock face accurately versus someone with dementia creating something that bears little resemblance to timepieces outside of Surrealist art.

And yet for all of its ubiquity, a significant amount of uncertainty surrounds the clock test. That’s the biggest takeaway from a recent article by Greg Uyeno at JSTOR Daily. As Uyeno writes, “there is no medical consensus on the details of the clock drawing test” — something that could open the door for a useful diagnostic tool to be incorrectly used.

Alternately, as neuropsychologist Cynthia Munro told Uyeno, “I sometimes wonder if its popularity exceeds how good it really is, because it’s one item.” That’s a running theme in the article: that this is only one diagnostic tool among many, and shouldn’t be used without other tests to diagnose a patient.

It’s worth pointing out that the clock drawing test is far from the only method of diagnosing cognitive issues. A 2018 study published in the Indian Journal of Psychological Medicine compared this method to the Mini-mental Status Examination in clinical settings. “Compared with the MMSE, it was found that the CDT lacks sensitivity and negative predictive value,” the authors wrote. “Thus, the CDT alone would not be ideally suited to use as an initial screening tool followed by more definitive testing if necessary.”

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With advances in AI technology and machine learning, the clock drawing test seems poised for a technological boost. It’s important to remember that this is, in fact, only one part of a larger diagnosis — and drawing a clock face well (or badly) can only indicate so much.