Does forcing a smile make you happier? The pen study that wouldn't repeat

Does forcing a smile make you happier? In 1988 Fritz Strack, Leonard Martin and Sabine Stepper ran what is arguably the most influential study on the question. It became a staple of introductory psychology classes.

The idea behind it, the facial feedback hypothesis, is rooted in Charles Darwin and William James. It says that your facial expression directly affects your emotional experience. Darwin wrote that the free expression of an emotion intensifies it, and that even the simulation of an emotion tends to arouse it.

The pen study tested this without telling participants. They were told the study was about how hard certain tasks are for people without the use of their hands or arms. Participants held a pen between their teeth, which forces a smile, or between their lips, which forces a frown, while viewing comedic cartoons. The group in the smiling position reported a higher humor response.

In 2016 a Registered Replication Report across 17 labs in different countries tried to reproduce it, and failed to reproduce the 1988 results. A later analysis by Noah and colleagues pointed to a methodological discrepancy, a camera pointed at participants, and reported replicating the original result when the camera was absent. A 2019 meta-analysis of 138 studies confirmed small but robust effects overall. Then a preregistered adversarial collaboration, the Many Smiles Collaboration, tested 3,878 people in 19 countries: copying a smiling face or deliberately smiling increased happiness, but the evidence was less conclusive for the pen-in-mouth task.

A strong version of the hypothesis, in which facial feedback decides whether emotion occurs, has not received substantial support. A weak version, in which expression plays a limited role, has.