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2016-02-25 11:03:41
Francesca Gino
February 23, 2016
You arrive at the office and, as usual, face a long list of tasks to
accomplish: getting back to your colleagues about joint projects, sending those
time-sensitive e-mails, finishing up that important performance review, making
progress on one project, deciding on next steps for another. What s the best
way to tackle your to-do list?
You may have devised a personal strategy to help you order your various tasks.
But if you are like most people, you may not give too much thought about when
is the best time to tackle each of them. You should. Recent research suggests
that you need to think more strategically about how the time of day affects
your decisions and performance.
Over the course of a regular day, everyone s mental resources get taxed,
research has consistently shown. Thus, as the day wears on, whether you like it
or not, you become increasingly fatigued and consequently more likely to
underperform on work tasks. Cognitive fatigue in a very common condition that
results from sustained engagement that taxes your mental resources. This seems
obvious, right? Yet the vast majority of people often overlook cognitive
fatigue, despite the fact that it influences their choices and behaviors in
profound ways.
Research has found that persistent cognitive fatigue results in burnout at
work, lower motivation, increased distractibility, and poor information
processing. It even lowers the quality of everyone s judgment and decisions,
including those of experts.
For instance, scientists Shai Danziger, Jonathan Levav, and Liora Avnaim-Pesso
analyzed 1,112 bench rulings in a parole court and plotted the proportion of
favorable rulings over the course of the day. They found that judges were more
likely to deny a prisoner s request and accept the status quo outcome as they
advanced through the sequence of cases on a given day. More specifically, their
proportion of favorable rulings started out high, at about 65% at the start of
the day, but dropped off rapidly.
By the time a meal break came around, the proportion of favorable rulings was
close to zero. When court was back in session, the pattern repeated itself,
starting high and ending with almost zero favorable rulings. Interestingly,
neither the judges nor the panelists who advised them were aware that mental
energy is essential to careful deliberation and the later in the day, the lower
such energy is, unless a lunch break allows judges to recharge.
Evidence for the same type of cognitive fatigue has been found in other
contexts, including consumers choosing among various products and physicians
prescribing antibiotics. Primary care doctors often prescribe unnecessary
antibiotics for acute respiratory infections (ARI), researchers have found. As
the physicians appeared to wear down during their morning and afternoon
clinic sessions, the rates at which they prescribed antibiotics increased.
About 5% more patients receive antibiotics at the end of a clinic session as
compared to the beginning, this research shows. Thus, while clinicians make
many patient care decisions each day, the cumulative demand of these decisions
leads to more inappropriate choices later in the day.
Considered together, this evidence points to a clear conclusion: The overall
demand of multiple decisions on people s cognitive resources throughout the day
erodes their ability to resist making easier and potentially inappropriate or
bad decisions.
Similarly, time of day can affect performance. Hans Henrik Sievertsen of the
Danish National Centre for Social Research, Marco Piovesan of the University of
Copenhagen, and I found that time of day affects students performance in
schools. Using test data on the full population of 8- to 15-year-old children
in Danish public schools from school years 2009/10 and 2012/13 a sample of
over two million data points we measured the effect of both time of day and
breaks on students performance on standardized tests. Consistent with our
predictions, cognitive fatigue led students to perform worse on the tests, and
breaks recharged their energy.
Specifically, our analyses led to three main findings:
The later in the day the time of the test was, the lower students performance
on the test
Breaks caused a significant improvement in performance
The effect of time of day and of breaks was not homogeneous that is,
low-performing students were more affected by breaks (and also by the time of
the day when the test was taken) than high-performing students
Importantly, a 20- to 30-minute break causes an improvement in test scores that
is larger than an hour s deterioration. So, if there were a break after every
hour, test scores would actually improve over the course of the day. But if
breaks occur only every other hour like they do in the Danish system, the total
effect is negative.
As this research on experts and students suggests, time of day and breaks have
a meaningful influence on your decisions, behavior, and performance. So as you
think through your to-do list, you may want to carefully consider the role of
these external factors. Make sure you tackle the tasks that require a great
deal of attention and mental energy earlier in the day and take breaks
throughout the day.
Francesca Gino is a professor at Harvard Business School, a faculty affiliate
of the Behavioral Insights Group at Harvard Kennedy School, and the author of
Sidetracked: Why Our Decisions Get Derailed, and How We Can Stick to the Plan
(Harvard Business Review Press, 2013). She cochairs an HBS executive education
program on applying behavioral economics to organizational problems. Twitter:
@francescagino.