Levels of Evidence

peer reviewed journal

where to find best evidence

impact factor

a measure of the frequency with which an average article in a

journal has been cited in a partcular year

‒ High

• Widely circulated

• Articles are accepted as quality artcle

• Considered as top-quality journal in its area of focus

levels of evidence

tradition - small circle

authority

experience

deductive ←→ inductive reasoning

scientific evidence - big circle

level of evidence characteristivs

• For consumers of research

• To determine the extent to which a partcular study is methodologically rigorous & relevant to a partcular client &/or practice setting

• Expected rigor for the design& control of bias, thereby indicatng the level of confdence that may be placed in the fndings

• ‘Rating’ system

‒Framework to organize perspectve

quantitiative research

• experiments — answering a question

• using the pyramid

qualitative rearch

• usually no hypothesis

• exploratory — open ended

cochrane levels of evidence

3 major criteria to determine the credibility of findings from a treatment or interventon

‒ Strength of the evidence

‒ Size of the effect

‒ Relevance of the evidence

*Also must consider research design

level of evidence (study design)

an estimate of certainty that the identified evidence is a true measure of the benefts of an intervention

quality of evidence

the extent to which researchers minimize bias in the study design by controlling for variables that could bias the results or the interpretaton of results

‒ Blinding, placebo effect, double-blinded, experimenter bias, observer bias

statistical precision

the accuracy with which the outcome or effect of the intervention was measured & estimated using appropriate statistical analyses

pyramid

• stronger study designs are at the top of the pyramid

• weaker study designs are at the bottom of the pyramid

grade up

• strong effect size

• strong design

grade down

• poor design, lack of the consistency with other studies

• small effect

level 1

systemic reviews

level 2

randomized trials

level 3

normalied controlled cohort and follow up studies

level 4

case series, case control, and histroically controlled studeis

level 5

mechanism based reasoning case studies

effect size

Degree to which a positve (or negatve) efect of an interventon exceeds the usual outcomes that would happen in the absence of the interventon

‒ Magnitude of a treatment effect

• it is not a measure of signifcance

‒ Not dependent on sample size

d statistic

ranges 0 (ineligible effect) to > 1.00 (large effect)

r statistic (Pearsons’s r, correlation coefficient)

positive/negative linear relationship

strength of association (< .3= small, .3-.5 =-0.2 medium, > .5 = large)

not

effect size is _ statisitcal significance

statistical significance

p value (dependent on sample size)

confidence interval

upper and lower limits of the true effect size

relevance of the evidence

Degree to which the assessment used to measure the effectiveness/harmfulness of an intervention is appropriate & useful for the people / problem under study

validity

measures what its supposed to measure

reliability

able to get the same scores from various people doing the study

qualitative research (levels of evidence)

Appraisal is not hierarchical

• Multdimensional

• Appraisal across 5 dimensions

‒ No single study will meet all requirements described in each of

the 5 dimensions

descriptive vividness

the degree to which the study methods & findings are clear, credible, complete, & valid

‒ A study must include essential descriptive information about the study background, purpose, & research questons

‒ Context is important to interpretation

methodological congruence

the extent of rigor in documentaton, procedures, & ethics

‒ Includes evidence of conformability, the description of the data collection process, & the decision rules & reasoning that went into decision-making & interpretation of the findings

analytical preciseness

congruence between study data, findings, interpretatons,theoretical linkages, & conclusions drawn

‒ The study hypotheses or propositons are verifable by the study data & presented as such in theresearch report