Doctors’ clinical judgement worsens as the day progresses due to ‘decision fatigue’, a US study has found.

To investigate how the time of day influences medical decision making, researchers looked at the rates of ordering of guideline-recommended cancer screening tests by physicians in 33 primary care practices.

They found that clinicians’ ordering rates of breast cancer screening tests was highest at 8 am ( 64%), decreased throughout the morning to 49% at 11 am, increased slightly to 56% at noon, and then decreased to 47.8% at 5 pm. A similar decline in test ordering patterns was seen for colorectal cancer screening, decreasing from 36.5% at 8 am to 31.3% by 11 am, increasing at noon to 34.4%, and then decreasing to 23.4% at 5pm.

The trend for decreasing test ordering as the day progressed was statistically significant, said researchers from Johns Hopkins University School of Medicine.

While some of the decline could be due to physicians falling behind schedule and having more rushed appointments, there was also likely also an element of  ‘decision fatigue’, they wrote in JAMA Network Open.

The researchers defined decision fatigue as “the depletion of self-control and active initiative that results from the cumulative burden of decision making”.

“In other words, as the day goes on, clinicians may be less likely to discuss cancer screening with patients simply because they have already done this (and made other decisions) a number of times”.

“As patients earlier in the day decline screening despite the clinician’s recommendation, it could influence how likely the clinician is to bring up the topic later in the day with a different patient.”

The researchers noted that similar daytime variations in physician decision making have been reported for physicians’ flu vaccination rates, which decreased as the day progressed, and for inappropriate prescribing of antibiotics and opioids, which increased later in the day.

“In each of these studies, behaviours improved slightly after lunch (a short break for most clinicians), as was the case in the current study,” they wrote.

The findings prompted an opinion article in the New York Times by Dr Jeffrey Linder, professor of medicine at Northwestern University, who wrote under the headline “Don’t Visit Your Doctor in the Afternoon”.

Describing how he alleviated his own “3 o’clock fade” with a snack and some coffee, Dr Linder said it was not surprising that when doctors became more fatigued “they defaulted to the easy thing” – for example, writing an antibiotic prescription rather than explaining why it wasn’t necessary.

‘Decision fatigue’ was well recognised by psychologists in other workplace environments, he wrote.

“We doctors like to think of ourselves –  and the public might like to think of us — as rational decision makers, but depending on the time of day, treatments change,” said Dr Lindner.

“Half the battle is knowing this exists, finding a plan to compensate and maybe taking a quick break.”