The aim of this chapter is to show which types of study are needed to answer particular questions, outline some hints for searching, and introduce the basic questions to address in critical appraisal.
On completion of this chapter the reader will be able to identify the most appropriate study design to answer questions, and be aware of the three basic questions to address in a critical appraisal.
If there are no evidence-based guidelines, Cochrane reviews or other systematic reviews to address our clinical problems then we must look to individual studies.
The type of study that we need to look for depends on the question that we need answered (see Table 7-1).
|Clinical problem||Most appropriate study design|
|Prognosis||Individual inception cohort study with ≥ 80% follow-up|
|Diagnosis||Validating cohort study with good reference standards|
|Differential diagnosis/symptom prevalence study||Prospective cohort study with good follow-up|
|Economic and decision analyses||Analysis based on clinically sensible costs or alternatives; systematic review(s) of the evidence; and including multi-way sensitivity analyses|
|Acceptability, appropriateness and quality of care, reasons for undergoing treatment||Qualitative studies|
Let us consider examples of the main question types:
What is the best type of restoration for carious primary molar teeth?
What is the best method of preventing root caries in adult patients?
What are the side-effects of using chlorhexidine mouthwash for the treatment of periodontal disease?
Are digital x-ray systems better at diagnosing caries than film-based systems?
Are school-based toothbrushing programmes cost-effective?
What are teenagers’ reasons for undergoing orthodontic treatment?
As before, you need to develop a PICO question for each of these questions (Table 7-2).