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.
When to see a doctor. If you have any signs or symptoms of a mental illness, see your primary care provider or mental health specialist. Most mental illnesses don't improve on their own, and if untreated, a mental illness may get worse over time and cause serious problems.ental illness symptoms can affect emotions, thoughts and behaviors. Examples of signs and symptoms include: 1  Feeling sad or down. 2  Confused thinking or reduced ability to concentrate. 3  Excessive fears or worries, or extreme feelings of guilt.