Evidence Table:

Level I: Evidence obtained from a systematic review of all relevant randomised controlled trials.

Level II: Evidence obtained from at least one properly designed randomised controlled trial.

Level III:

1. Evidence obtained from well-designed controlled trials without randomisation.

2. Evidence obtained from well-designed cohort or case control analytic studies, preferably from more than one centre or research group.

3. Evidence obtained from multiple time series, with or without the intervention. Dramatic results in uncontrolled experiments.

Level IV: Opinion of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees.

Source: The Joanna Briggs Institute (as cited in Reilly, Douglas & Oates, 2004).

Reilly, S., Douglas, J. & Oates, J. (Eds.) (2004). Evidence-base practice in speech pathology. London: Whurr Publishers.