Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Measurement This study assessed frustration using the four-item scale of Kammann and Flett [1983] and continuance intention using the three-item scale of Bhattacherjee and Premkumar [2004]. Intensity of gamer experience was measured using the item “On average, how many hours per week do you spend playing this game?”.
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