The study of SWB is a central concern of positive psychology .  Positive psychology was founded by Seligman and Csikszentmihalyi (2000) who identified that psychology is not just the study of pathology, weakness, and damage; but it is also the study of strength and virtue.  Researchers in positive psychology have pointed out that in almost every culture studied the pursuit of happiness is regarded as one of the most valued goals in life. Understanding individual differences in SWB is of key interest in positive psychology, particularly the issue of why some people are happier than others. Some people continue to be happy in the face of adversity whereas others are chronically unhappy at the best of times.  Additionally, positive psychology has investigated how people might improve their level of SWB and maintain these improvements over the longer term, rather than returning to baseline.  Lyubomirsky (2001) argued that SWB is influenced by a combination of personality/genetics (studies have found that genetic influences usually account for 35-50% of the variance in happiness measures), external circumstances, and activities that affect SWB.  She argued that changing one's external circumstances tends to have only a temporary effect on SWB, whereas engaging in activities (mental and/or physical) that enhance SWB can lead to more lasting improvements in SWB.