Dr. ramos is interested in studying how indoor lighting can influence people's moods during the winter. a sample of 100 households is selected. fifty of the homes are randomly assigned to the bright-light condition where dr. ramos replaces all the lights with 100-watt bulbs. in the other 50 houses, all the lights are changed to 60-watt bulbs. after two months, dr. ramos measures the level of depression for the people living in the houses. assuming that the study uses people from different age groups, participant age would be a(n) variable in the experiment.