Stratified sampling is often used when one or more of the stratums in the population have a low incidence relative to the other stratums. Convenience sampling is used in exploratory research where the researcher is interested in getting an inexpensive approximation of the truth.
Sometimes symptoms of a mental health disorder appear as physical problems, such as stomach pain, back pain, headache, or other unexplained aches and pains.
Common diagnosis of mental illness, under the category of anxiety disorders, includes: 1  Panic disorder. 2  Obsessive-compulsive disorder (OCD) 3  Post-traumatic stress disorder (PTSD)  Social phobia (social anxiety 1  disorder) Generalized anxiety disorder  (GAD)