Hospital floors are usually covered by bare tiles. carpets would cut down on noise but might be more likely to harbor germs. to study this possibility, investigators randomly assigned 8 of 16 available hospital rooms to have carpet installed. the others were left bare. later, air from each room was pumped over a dish of agar (a gelatinous substance obtained from various kinds of red seaweed and used in biological culture media). the dish was incubated for a fixed period, and the number of bacteria colonies were counted. the response variable in this experiment is