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.
The list of types of Mental illness mentioned in various sources includes: 1  Depressive disorders. 2  Depression. 3  Dysthymic disorder. 4  Bipolar disorder. 5  Cyclothymic disorder. 6  Anxiety disorders. 7  Panic disorder. 8  Social phobia. 9  Specific phobias.