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.
Get the facts on common mental disorders, such as those related to anxiety, attention deficit, conduct, depression, schizophrenia, and trauma. The following are descriptions of the most common categories of mental illness in the United States. Anxiety disorders are characterized by excessive fear or anxiety that is difficult to control and negatively and substantially impacts daily functioning.