An interesting finding showing that emotional closeness affects mimicking yawning: we tend to yawn when the people we like yawned. However, the study cited is an observational design so it cannot control sleepiness effect. Use it as an example of research design.
For the past several decades researchers have been studying the ways in which the body reveals properties of the mind. An important subset of this work has taken this idea a step further: do the ways our bodies relate to one another tell us about the ways in which our minds relate to one another?
Many studies have found that we quite readily mimic the nonverbal behavior of those with whom we interact. Furthermore, the degree to which we mimic others is predicted by both our personality traits as well as our relationship to those around us. In short, the more empathetic we are, the more we mimic, and the more we like the people we’re interacting with, the more we mimic.
The bulk of this research has made use of clever experimental manipulations involving research assistant actors. The actor crosses his legs and then waits to see if the participant crosses his legs, too. If so, we’ve found mimicry, and can now compare the presence of mimicry with self-reports of, say, liking and interpersonal closeness to see if there is a relationship.
Past work has demonstrated that, similar to behavioral mimicry, contagious yawners tend to be higher in dispositional empathy. That is, they tend to be the type of people who are better, and more interested in, understanding other people’s internal states.
To test this hypothesis the researchers observed the yawns of 109 adults in their natural environments over the course of a year. When a subject yawned the researchers recorded the time of the yawn, the identity of the yawner, the identities of all the people who could see or hear the yawner (strangers, acquaintances, friends, or kin), the frequency of yawns by these people within 3 minutes after the original yawn, and the time elapsed between these yawns and the original yawn. In order to rule out alternative explanations for any contagion the researchers also recorded the position of the observers relative to the yawner (whether they could see or only hear the yawn), the individuals’ gender, the social context, and their nationality.
Sure enough, yawn contagion was predicted by emotional closeness. Family members showed the greatest contagion, in terms of both occurrence of yawning and frequency of yawns, and strangers and acquaintances showed a longer delay in the yawn response compared to friends and kin. No other variable predicted yawn contagion.