There are at least two important factors to keep in mind when assessing a systematic review.
Publication of a study in a peer-reviewed scientific journal is not a guarantee of quality. Individual studies are generally assessed along two dimensions: level of evidence and study quality. Level of evidence refers to the establishment of a hierarchy of study designs based on the ability of the design to protect against bias. Although there is no one universally accepted hierarchy, randomized controlled trials (RCTs) are considered to be the design least susceptible to bias, and various hierarchies follow from there through observational studies and non-experimental designs. The table below is one example of a hierarchy of levels of evidence.
Levels of Evidence
|1++||High quality meta-analyses, systematic reviews of RCTs, or RCTs with a very low risk of bias|
|1+||Well-conducted meta-analyses, systematic reviews, or RCTs with a low risk of bias|
|1-||Meta-analyses, systematic reviews, or RCTs with a high risk of bias|
High quality systematic reviews of case control or cohort or studies
|2+||Well-conducted case control or cohort studies with a low risk of confounding or bias and a moderate probability that the relationship is causal|
|2-||Case control or cohort studies with a high risk of confounding or bias and a significant risk that the relationship is not causal|
|3||Non-analytic studies, e.g. case reports, case series|
Adapted from the Scottish Intercollegiate Guidelines Network.
Study quality is an assessment of the extent to which a study, of whatever design, was designed and implemented appropriately. Again, there is no single universally accepted set of criteria for what constitutes a high quality study. For examples of study quality criteria, see the Scottish Intercollegiate Guidelines Network.
Expert Opinion Statements come from three areas:
Expert opinion can also be subjective statements or commentary with supporting reference(s).
Source: ASHA Practice Portal statement on the use of evidence
The examination of outcomes measures is recommended when describing client/patient/caregiver values to reflect the interests, values, needs and choices of the individuals served.