The Colorado Division of Wildlife caught 41 bighorn sheep on Mt. Evans and gave each one an injection to prevent heartworm. A year later, 38 of these sheep did not have heartworm, while the other three did. This is an experiment because a treatment was deliberately imposed on the individuals in order to observe a possible change in the response or variable being measured. This is an observational study because a treatment was deliberately imposed on the individuals in order to observe a possible change in the response or variable being measured. This is an experiment because observations and measurements of individuals are conducted in a way that doesn't change the response or the variable being measured. This is an observational study because observations and measurements of individuals are conducted in a way that doesn't change the response or the variable being measured