Chapter 6 - Levels of Evidence

Question 1

What are the major clinical questions in healthcare?

Answer 1

• Health professionals face clinical questions in daily practice (e.g., does limb positioning after knee-replacement surgery affect range of motion).
• Evidence from research answers clinical questions.
• Not all research evidence is of equal strength, and bias affects the trustworthiness of the evidence (validity).
• Levels of evidence relate to the level of bias, with higher levels indicating lower risk of bias

Question 2

What are the different study design?

Answer 2

Each clinical question has a study design:
- Intervention
- Diagnostic
- Aetiological
- Prognostic
- Screening Intervention

Question 3

How are clinical questions organised into levels of evidence according to their risk of bias?​

Answer 3

• Each level of evidence I, II, III, IV indicates the degree of risk for bias of a study’s design
• Level I is high quality evidence and has a low risk of bias - a systematic review of Level II studies ( Randomised Control Trial – RCT)
• Level IV is lower quality evidence and has a higher risk of bias

Question 4

How does bias threaten the validity of research evidence?​

Answer 4

• Bias is a consistent error in results and conclusions.
• Random allocation can minimize bias, but systematic reviews are vulnerable to bias from the original studies they include.
• Well-designed research and careful systematic reviews are essential to reduce bias and enhance validity.

Question 5

What are the grades of recommendation for evidence, leading to clinical practice guidelines?​​

Answer 5

The NHMRC uses the GRADE system to evaluate evidence in clinical practice guidelines, assessing both the quality of evidence and the strength of recommendations as strong, weak, conditional, or discretionary.

Question 6

How do levels of evidence fit into a general hierarchy of evidence?

Answer 6

• Primary evidence comes from original studies (Levels II, III, IV), while secondary evidence comes from systematic reviews (Level I).
• Meta-analysis, used in some systematic reviews, combines and analyzes results from multiple quantitative studies. Systematic reviews and clinical practice guidelines represent the highest levels of evidence.