The validity of the information can vary by the type of the study.
There is need to identify the essential issues of validity for the 4 main types of questions:
Types of questions explained
Therapy: How to select treatments to offer patients that do more harm and that are worth the efforts and cost of using them
Diagnosis: When considering the possible causes of a patient’s clinical problem
Prognosis: How to estimate the patients likely clinical course over time and anticipate likely complications of the disease.
Cause/Etiology: How to identify causes for disease.