by 
Klaus Vedfelt
An unfortunate feature of science is that two experiments that apparently look at the same thing can produce different results. Often the various results are greeted unhelpfully as the experiments—and sometimes even the entire field—are accused of being junk. A more useful answer is to consider whether the experiments, while looking at the same thing, might not be identical. And if they are not, whether the differences between them can tell us something.
A new study in Nature Human Behavior describes a subtle way some psychological experiments can deviate: if they include breaks to allow participants to avoid getting tired. Forced breaks can cause people’s spirits to drop and continue to drop if the break drags on. And since mood affects behavior in a variety of other psychological tests, this has the potential to have a complicating influence on a wide range of studies.
Waiting is the hardest part
The work began with an incredibly simple discovery. Most studies operate under the assumption that a participant’s mood remains relatively stable throughout an experiment. But the researchers here asked participants to rate their mood at the start and end of the experiments – and thus at the start and end of the breaks between experiments. The researchers noticed that mood decreased fairly consistently during the break. After a roughly 10-minute break, people rated their mood as more than 20 percent lower than when the break started.
At this point, the researchers decided that the effect, which they call “mood drift over time” was worth looking into. So they took various steps to ensure the quality of their work, pre-registering the study designs and getting many participants involved in replication experiments. In all, almost 30,000 participants, both adults and youth, took part in these experiments.
Some of these tests ruled out the possibility that people’s mood worsened from being repeatedly prompted about their mood. And they tried several different mood assessment methods and found that the details didn’t make a difference: mood worsened no matter how they asked. They also received a mood test from many people who played a risk game on a mobile app. People did it for fun, so the effect was less, but being told to wait between games made people feel down.
The one instance they found that didn’t make people feel worse was replacing the forced break with telling people they could go off and do whatever they wanted for seven minutes. Although the self-reported activities were quite small – things like standing up, thinking and skimming the news were prominent – this was enough to avoid a statistically significant change in the participants’ mood.
Operation
The latest result suggests that it’s not so much inactivity as loss of agency that bothered people. Loss of agency is also a factor in boredom, which may seem to explain the decline in mood. But an experiment that also asked people to rate their boredom showed that while there is some overlap between boredom and mood swings, the former doesn’t fully account for the latter.
By looking at participants who were involved in more than one of these studies, the researchers also found that the magnitude of the mood swing was fairly consistent within an individual over time, suggesting that the effect may be at least partly a stable personality trait.
Finally, the researchers showed that this spills over into behavioral tests. There are many tests that look at risk tolerance; the tests can implement a combination of high probability/low payout or a high risk/high payout game. Using one of these tests, the researchers found that people were less likely to gamble after experiencing mood swings.
Overall, the researchers present their work as a warning. It is likely that there is a wide range of behaviors influenced by our general mood, and many of them have probably been the subject of experiments. Sentiment bias means that the exact structure of the experimental routine can affect the outcome of these experiments, even if the exact same tests are used. In other words, it can explain why two apparently similar studies can produce different results.
It may also go a long way to explaining why people hate being forced to sit still in a room.
Nature Human Behavior, 2023. DOI: 10.1038/s41562-023-01519-7 (About DOIs).
