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1Levels of Evidence For Primary Research Question
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Level-I through IV studies may be graded downward on the basis of study quality, imprecision, indirectness, or inconsistency between studies or because the effect size is very small; these studies may be graded upward if there is a dramatic effect size. For example, a high-quality randomized controlled trial (RCT) should have >80% follow-up, blinding, and proper randomization. The Level of Evidence assigned to systematic reviews reflects the ranking of studies included in the review (i.e., a systematic review of Level-II studies is Level II). A complete assessment of the quality of individual studies requires critical appraisal of all aspects of study design.
Reprinted with permission. Copyright © 2015 by The Journal of Bone and Joint Surgery, Incorporated.
| Study Type | Question | Level I | Level II | Level III | Level IV | Level V |
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| Diagnostic –Investigating a diagnostic test | Is this (early detection) test worthwhile? Is this diagnostic or monitoring test accurate? |
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| Prognostic –Investigating the effect of a patient characteristic on the outcome of a disease | What is the natural history of the condition? |
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| Therapeutic – Investigating the results of a treatment | Does this treatment help? What are the harms |
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| Economic | Does the intervention offer good value for dollars spent? | Computer simulation model (Monte Carlo simulation, Markov model) with inputs derived from level I studies, lifetime time duration, outcomes expressed in dollars per quality-adjusted life year’s (QALYs) and uncertainty examined using probabilistic sensitivity analyses | Computer simulation model (Monte Carlo simulation, Markov model) with inputs derived from level II studies, lifetime time duration, outcomes expressed in QALYs and uncertainty examined using probabilistic sensitivity analysis | Computer simulation model (Monte Carlo simulation, Markov model) with inputs derived from level II studies, relevant time horizon, less than lifetime, outcomes expressed in QALYs and uncertainty examined using stochastic multilevel sensitivity analysis | Decision tree over the short time horizon with inputs data for original level-II and III studies and uncertainty as examined by univariate sensitivity analysis | Decision tree over the short time horizon with inputs data informed by prior economic evaluation and uncertainty as examined by univariate sensitivity analysis |
1 Level-I through IV studies may be graded downward on the basis of study quality, imprecision, indirectness, or inconsistency between studies or because the effect size is very small; these studies may be graded upward if there is a dramatic effect size. For example, a high-quality randomized controlled trial (RCT) should have >80% follow-up, blinding, and proper randomization. The Level of Evidence assigned to systematic reviews reflects the ranking of studies included in the review (i.e., a systematic review of Level-II studies is Level II). A complete assessment of the quality of individual studies requires critical appraisal of all aspects of study design.
2 Investigators formulated the study question before the first patient was enrolled.
3 In these studies, “cohort” refers to a nonrandomized comparative study. For therapeutic studies, patients treated one way (e.g., cemented hip prosthesis) are compared with those treated differently (e.g., cementless hip prosthesis).
4 Investigators formulated the study question after the first patient was enrolled.
5 Patients identified for the study on the basis of their outcome (e.g., failed total hip arthroplasty), called “cases,” are compared with those who did not have the outcome (e.g., successful total hip arthroplasty), called “controls.”
6 Sufficient numbers are required to rule out a common harm (affects >20% of participants). For long-term harms, follow-up duration must be sufficient.
