Even if research evidence has internal validity, it often applies to the ‘ideal’ patient who has been selected for a clinical trial, and estimates an ‘average’ benefit for that patient. However, to decide whether you can apply that evidence to your patient, you must consider:
- that individual’s characteristics, preferences, values
- the environment in which you practice
- the practitioner’s expertise and familiarity with an intervention
You are now looking at external validity.
Before extrapolating beyond the trial, ask yourself these questions:
- Are the results clinically important?
- Do the results apply to my patient?
- What are my patients’ values and preferences?
- Can this practice be implemented in this healthcare setting?
- How can I help my patient make a decision?