Your Behavior May Reflect Your Socioeconomic Status (SES)?

There is an interesting research conducted by Kraus and Keltner (2009) proposes that people who come from higher SES family are very likely to show disengagement behavior while who are from lower SES family tend to show engagement cues while talking to strangers. Below is the abstract of the research:

Socioeconomic status (SES) is a primary determinant of health vulnerabilities and social affiliations. To ascertain if SES is signaled in brief patterns of nonverbal behavior, we had participants of varying SES backgrounds engage in a brief interaction with a stranger. Videos of 60-s slices of these interactions were coded for nonverbal cues of disengagement and engagement, and estimates of participants' SES were provided by naive observers who viewed these videos. As predicted by analyses of resource dependence and power, upper-SES participants displayed more disengagement cues (e.g., doodling) and fewer engagement cues (e.g., head nods, laughs) than did lower-SES participants. Results were also consistent with the thin-slicing literature, in that observers' estimates of SES were reliable with each other and accurately predicted targets' family income, maternal education, and subjective SES. Finally, nonverbal displays of disengagement and engagement predicted observers' estimates of SES, which suggests that these cues are systematic signs of SES. These results have implications for understanding the effect of SES on social interactions and patterns of disengagement and engagement in other realms.

Their theoretical background is that higher SES people would be less likely to be dependent on the others because they already have more resources than the lower SES people. This theory sounds like people being engaged with the others is just to serve their survival purpose, seems something like evolutionary theory. I do agree that sometimes people being engaged in a conversation because they want to get something from their target, however it does not mean that this could be generalized to everyone and every social setting. Can't I talk to people attentively simply because I am interested in the people? Can't I being sociable or aggreable due to my personality (of course, "I" definitely does not mean Chee Khong)? Thus I think it would be better if this research could include the other variables such as personality, emotion, and intention of the participants.

Reference:
Kraus, M. W. & Keltner, D. (2009). Signs of Socioeconomic Status: A Thin-Slicing Approach. Psychological Science, 20, 99-106.