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.
Signs and symptoms of mental illness can vary, depending on the disorder, circumstances and other factors. Mental illness symptoms can affect emotions, thoughts and behaviors. Examples of signs and symptoms include: Feeling sad or down. Confused thinking or reduced ability to concentrate. Excessive fears or worries, or extreme feelings of guilt. Extreme mood changes of highs and lows. Withdrawal from friends and activities.