The scientific evidence is mixed as to whether companionship of a dog can enhance human physical health and psychological wellbeing. Studies suggesting that there are benefits to physical health and psychological wellbeing have been criticised for being poorly controlled, and finding that "[t]he health of elderly people is related to their health habits and social supports but not to their ownership of, or attachment to, a companion animal." Earlier studies have shown that people who keep pet dogs or cats exhibit better mental and physical health than those who do not, making fewer visits to the doctor and being less likely to be on medication than non-guardians.