The truth is, this question will never have a solid answer because people are people, everyone is different, and the mind is not something you can study concretely; however one can attempt to answer it by studying correlations and patterns in mental health and human behavior of both groups likewise. Studies have shown that people who are religious may be more protected from depression as they have been noted to have thicker brain stems (this goes more into biological psychology, but structures of the brain are able to help with psychological diagnoses). Meanwhile, other studies have shown that people who consider themselves spiritual but not religious are 19% more likely to develop psychological disorders than their religious and nonreligious counterparts. People who fall in the grey between the black and white that is theism and atheism are more prone to mental illness. Another study showed that there was an inverse correlation between a greater level of education and smaller religious population as time progresses. Because people are learning more and more about the world and science is beginning to explain so many things that religion once offered an unsupported answer for, the number of religious people keeps declining. People just don 't seem to "need" God as much as they used to. These are just three studies, but all three give different insight or answer this central question
The truth is, this question will never have a solid answer because people are people, everyone is different, and the mind is not something you can study concretely; however one can attempt to answer it by studying correlations and patterns in mental health and human behavior of both groups likewise. Studies have shown that people who are religious may be more protected from depression as they have been noted to have thicker brain stems (this goes more into biological psychology, but structures of the brain are able to help with psychological diagnoses). Meanwhile, other studies have shown that people who consider themselves spiritual but not religious are 19% more likely to develop psychological disorders than their religious and nonreligious counterparts. People who fall in the grey between the black and white that is theism and atheism are more prone to mental illness. Another study showed that there was an inverse correlation between a greater level of education and smaller religious population as time progresses. Because people are learning more and more about the world and science is beginning to explain so many things that religion once offered an unsupported answer for, the number of religious people keeps declining. People just don 't seem to "need" God as much as they used to. These are just three studies, but all three give different insight or answer this central question