Diabetes and Pollution Diabetes tends to be more prevalent in urban populations, but why this is so is not fully understood. A recent study on mice was designed to investigate the link between diabetes and air pollution. The study involved 28 mice, with 14 randomly selected to have filtered air pumped into their cage while the other 14 breathed particulate matter that simulated common air pollution. The response variable is the amount of insulin resistance each mouse had after 24 weeks. Higher insulin resistance indicates a greater risk for developing diabetes. Data recreated from information in Sun et al. "Ambient Air Pollution Exaggerates Adipose Inflammation and Insulin Resistance in a Mouse Model of Diet-Induced Obesity", Journal of the American Heart Association, 2009; 119 (4): 538-546. (a) Is this an observational study or randomized experiment