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Instructions for Authors

        Tabled 1Levels of Evidence for Primary Research
        A complete assessment of the quality of individual studies requires critical appraisal of all aspects of the study design.
        Types of Studies
        Therapeutic Studies-Investigating the Results of TreatmentPrognostic Studies-Investigating the Effect of a Patient Characteristic on the Outcome of DiseaseDiagnostic Studies- Investigating a Dignostic TestEconomic and Decision Analyses-Developing an Economic or Decision Model
        Level I
        • High-quality randomized controlled trial with statistically significant difference or no statistically significant difference but narrow confidence intervals
        • Systematic review
          A combination of results from two or more prior studies.
          of Level-I randomized controlled trials (studies were homogeneous
          Studies provided consistent results.
          )
        • High-quality prospective study
          Study was started before the first patient enrolled.
          (all patients were enrolled at the same point in their disease with ≥80% follow-up of enrolled patients)
        • Systematic review
          A combination of results from two or more prior studies.
          of Level-I studies
        • Testing of previously developed diagnostic criteria in series of consecutive patients (with universally applied reference “gold” standard)
        • Systematic review
          A combination of results from two or more prior studies.
          of Level-I studies
        • Sensible costs and alternatives; values obtained from many studies; multi-way sensitivity analyses
        • Systematic review
          A combination of results from two or more prior studies.
          of Level-I studies
        Level II
        • Lesser-quality randomized controlled trial (e.g., <80% follow-up, no blinding, or improper randomization)
        • Prospective
          Study was started before the first patient enrolled.
          comparative study
          Patients treated one way (e.g., with cemented hip arthroplasty) compared with patients treated another way (e.g., with cementless hip arthroplasty) at the same institution.
        • Systematic review
          A combination of results from two or more prior studies.
          of Level-II studies or Level-I studies with inconsistent results
        • Retrospective
          Study was started after the first patient enrolled.
          study
        • Untreated controls from a randomized controlled trial
        • Lesser-quality prospective study (e.g., patients enrolled at different points in their disease or <80% follow-up)
        • Systematic review
          A combination of results from two or more prior studies.
          of Level-II studies
        • Development of diagnostic criteria on basis of consecutive patients (with universally applied reference “gold” standard)
        • Systematic review
          A combination of results from two or more prior studies.
          of Level-II studies
        • Sensible costs and alternatives; values obtained from limited studies; multi-way sensitivity analyses
        • Systematic review
          A combination of results from two or more prior studies.
          of Level-II studies
        Level III
        • Case-control study
          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., had a successful total hip arthroplasty), called “controls.”
        • Retrospective
          Study was started after the first patient enrolled.
          comparative study
          Patients treated one way (e.g., with cemented hip arthroplasty) compared with patients treated another way (e.g., with cementless hip arthroplasty) at the same institution.
        • Systematic review
          A combination of results from two or more prior studies.
          of Level-III studies
        • Case-control study
        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., had a successful total hip arthroplasty), called “controls.”
        • Study of nonconsecutive patients (without consistently applied reference “gold” standard)
        • Systematic review
          A combination of results from two or more prior studies.
          of Level-III studies
        • Analyses based on limited alternatives and costs; poor estimates
        • Systematic review
          A combination of results from two or more prior studies.
          of Level-III studies
        Level IVCase series
        Patients treated one way with no comparison group of patients treated another way.
        Case series
        • Case-control study
        • Poor reference standard
        • No sensitivity analyses
        Level VExpert opinionExpert opinionExpert opinionExpert opinion
        1 A complete assessment of the quality of individual studies requires critical appraisal of all aspects of the study design.
        2 A combination of results from two or more prior studies.
        3 Studies provided consistent results.
        4 Study was started before the first patient enrolled.
        5 Patients treated one way (e.g., with cemented hip arthroplasty) compared with patients treated another way (e.g., with cementless hip arthroplasty) at the same institution.
        6 Study was started after the first patient enrolled.
        7 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., had a successful total hip arthroplasty), called “controls.”
        8 Patients treated one way with no comparison group of patients treated another way.
        Reprinted with permission. Copyright c 2005 by The Journal of Bone and Joint Surgery, Incorporated.