Multiple rewards may be averaging, rather than additive

On Hallowe’en, twenty-eight trick-or-treaters with the average age of around ten came to the house. All the kids were given different combinations of candy and asked to rate their happiness levels in relation to it. Seven different happiness levels were shown by using smiley face symbols ranging from neutral to open-mouthed-grin smiley face’. *Some kids were given a full-size Hershey’s chocolate bar, some kids were given a piece of gum, some kids were given first a Hershey’s bar then a piece of gum, and some kids were given first a Hershey’s bar then another Hershey’s bar. You would expect more candy to equal more happiness. But the children getting a chocolate bar then a piece of gum were less happy than the kids who received just the chocolate bar. And two chocolate bars did not bring more happiness than one chocolate bar.