10. Goldberg and Williams' (1988) General Health Questionnaire (GHQ) is a 12-item in- strument that measures psychological distress such as depression and anxiety. Scores could range from 0 to 36, with lower scores reflecting lower levels of distress. Let's assume the national mean GHQ score for aircraft maintenance technicians (AMTS) is =28, and you propose that if AMTS were to listen to music during their shift, their level of distress would be lower than the national average. For this study, the treat- and the parameter of interest is ment is

a. listening to music, AMTS

b. AMTS, GHQ scores C. AMTs, mean

d. listening to music, mean