The premise of this combination of two studies was:

“Emotional understanding is the central problem of human interaction.”

The researchers reanalyzed a 2008 study’s data, supplemented it with their own 2015 study, and found:

“Social-historical factors..explain cross-cultural variation in emotional expression and smile behavior.

We also report an original study of the underlying states that people believe [my emphasis] are signified by a smile.”

The researchers presented the subjects with a survey that asked them to rate 15 possible reasons for a person to smile at them on a seven-point scale of -3 to +3 for disagreeing/agreeing.

The research methodology didn’t take the additional necessary steps of establishing paired experiments that included presenting a similar survey to a control group of subjects to self-report their emotional motivations for smiling, and then processing the two surveys.

Did the study’s reviewer have anything to say about this lack of validation of the subjects’ beliefs to any factual measurements of a stranger’s corresponding “emotional expression and smile behavior?”

This combination of studies didn’t inform us about the “emotional understanding is the central problem of human interaction” premise. The researchers only provided evidence that the subjects’ cultures were one of many causal factors for the subjects’ beliefs about a hypothetical stranger’s smiling behavior.

The combined studies didn’t contain any emotional content to establish experimental conditions toward the goal of “emotional understanding.” No emotions were involved, for example, when a subject rated “strongly agree” to the “Wants you to like them” reason on a survey for a hypothetical stranger’s smiling behavior.

The studies didn’t show that the subjects rating their beliefs contributed to their real “emotional understanding.” Including emotional content, such as experimentally evoking an actual emotion in response to an actual stranger smiling, possibly could have contributed to real “emotional understanding.”

Research that strips out emotional content can’t factually provide evidence for real “emotional expression and smile behavior.” The degrees to which beliefs about and perceptions of a stranger’s smiling actually match their emotional reality remain to be shown.

http://www.pnas.org/content/112/19/E2429.full “Heterogeneity of long-history migration explains cultural differences in reports of emotional expressivity and the functions of smiles”