Starbucks gift cards are used in a study to encourage people, particularly introverts, to engage in social interactions. The study found that even when forced into social situations, introverts often reported higher levels of happiness than they predicted.
"Mentioned in context of the study as a gift reward of $10 to force people into social settings. The study demonstrates how introverts felt about being social and whether the rewards of the gift was equal to socializaiton."