Evaluation of device safety is often based on animal studies that provide valid scientific evidence (21 CFR 860.7(d)), and whether or not a facility has adequate standard operating procedures to ensure the quality and integrity of the data (21 CFR 58.81). FDA recommends that animal studies include adequate controls to minimize experimental variability and error. Such research controls include, but are not limited to, the minimization of anything given to or affecting the test animal in the course of an experiment that would impact the comparison between the test animals (i.e. animals receiving the test article) and control animals (i.e. animals receiving the control article). Variables that may impart change to the test animals may be devices other than the test article, or they may consist of background factors such as environmental factors, concomitant medications, or co-morbidities. You should minimize these confounding factors because they may hinder the ability of the investigator and FDA to clearly associate adverse or positive outcomes with the device and/or its effects.