You need to be a little more specific. Are you speaking of a psychological exam in terms of seeing if someone is suited for a specific job? Checking specifically on someone's mental status?
In the US, the psychiatrist is either an MD or DO that has completed medical school and a 4 year residency. They can prescribe medications, hospitalize patients, etc.
The clinical psychologist has a PhD in psych and has done a one year internship at a hospital, but is not able to write for any medications.
Hoep that this helps, not sure exactly what you are looking for.........