In order to measure happiness, most researchers use

A) PET scans, to look for evidence of activity in the amygdala.
B) the Positive Psychology Index.
C) a measure of subjective well-being.
D) behavioral observations of smiling.

Most researchers use a measure of subjective well-being as a way to measure happiness. This typically includes self-report measures of life satisfaction, positive affect, and negative affect. This approach to measuring happiness takes into account the individual's own perspective and feelings. PET scans are costly and not practical for large-scale studies, the Positive Psychology Index is not a commonly used measure among researchers, and behavioral observations of smiling may not necessarily indicate happiness.