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.
Mental Health Problem Symptoms, Causes and Effects. Mental health problems can cover a broad range of disorders, but the common characteristic is that they all affect the affected personâs personality, thought processes or social interactions. They can be difficult to clearly diagnose, unlike physical illnesses.