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Updated: May 7 2023

Clinical Trial Design


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Images types.jpg
  • Introduction
    • Clinical trial design impacts Level of Evidence
    • Clinical trials may be either observational or experimental
      • observational
        • researchers observe patient groups without allocation of intervention
        • may be either prospective or retrospective
        • may be descriptive or analytic
          • descriptive
            • useful for obtaining background information for more advance studies
            • examples
              • case reports
              • case series
              • cross-sectional studies
          • analytic
            • explores the association between a given outcome and a potentially related variable
            • examples
              • case-control
              • cohort
              • meta-analysis
      • experimental
        • researchers allocate treatment
        • allows the evaluation of efficacies of therapeutic interventions
        • examples
          • double-blinded, prospective, randomized clinical trial is the gold standard for evidence based medicine
    • Conflict of interest statement
      • submitted with each publication for each author
        • discloses all financial interests of each author as it relates to the study and/or publication 
  • Randomized controlled trial 
    • Definition
      • a study in which patients are randomly assigned to the treatment or control group and are followed prospectively
      • provides the most compelling evidence that the study treatment causes the expected effect on human health
      • randomization minimizes study selection bias
      • by definition an experimental study because there is an intervention
    • Study designs
      • parallel-group
        • each participant is randomly assigned to a group, and all the participants in the group receive (or do not receive) an intervention,
      • crossover
        • administration of two or more therapies, one after the other, in a random order
        • susceptible to bias if washout period is inadequate
      • factorial
        • each participant is randomly assigned to a group that receives a particular combination of interventions or non-interventions.
      • cluster
        • pre-existing groups of participants (e.g., villages, schools) are randomly selected to receive (or not receive) an intervention.
    • Blinding
      • blinding of the outcome assessor
        • likely to decrease the treatment effect reported in the study 
    • Analysis
      • intent-to-treat analysis
        • outcomes based on the group into which they were randomized, regardless of whether the patient actually received the planned intervention
        • minimizes non-responder bias
      • as-treated analysis
        • outcomes based on actual intervention received, regardless of which group their were randomized to.
        • by definition, when as-treated analysis is done, the results are no longer a RCT
        • used when there is higher cross-over from randomization groups (e.g., a patient is randomized to nonoperative treatment, but elects to obtain surgical treatment).
      • per protocol
        • excludes patients who were not compliant with the protocol guidelines
    • Example
      • you want to determine whether your new toothpaste prevents cavities better than your old toothpaste. You randomly assign a large number of patients to either an intervention group, which uses the new toothpaste, or to a control group, which uses the old toothpaste. You would then measure the amount of cavities between the groups over time.
    • Orthopaedic Literature Examples
  • Cohort study
    • Definition
      • a study in which patient groups are separated non-randomly by exposure or treatment, with exposure occurring after (prospective), or before (retrospective), the initiation of the study
    • Evidence
      • 217480Level II or III evidence
    • Analysis
      • results usually reported as relative-risk
    • Example
      • you want to determine if smoking is a risk factor for the development of lung cancer. You identify a group of smokers and a group of non-smokers, and follow them over time measuring the desired outcome, in this case, lung cancer.
    • Orthopaedic Literature Examples
  • Case-control study
    • Definition
      • a study in which patient groups are separated by the current presence (cases) or absence (controls) of disease and examined for the prior exposure of interest
    • Evidence
      • Most are Level III evidence
    • Analysis
      • usually reported as odds-ratio
    • Example
      • you want to determine if smoking is a risk factor for the development of lung cancer. You compare the smoking history of individuals with lung cancer (cases) and those without (controls).
    • Orthopaedic Literature Examples
  • Meta-analysis
    • Definition
      • a systematic review that summarizes results of other studies
    • Evidence
      • may be used to increase the statistical power of several under-powered studies
    • Example
      • you want to determine if wearing sunscreen results in fewer cases of melanoma. You pool the results of 9 randomized controlled studies and statistically analyze the data to determine the effect of the relationship.
    • Orthopaedic Literature Examples
  • Cross-sectional Study
    • Definition
      • study group is analyzed at a given time ("snapshot") with no follow-up
    • Example
      • you want to determine the prevalence of baseball injuries during the 2003 little-league season
    • Orthopaedic Literature Examples
  • Case Series
    • Definition
      • a retrospective account of multiple patients with the same injury or treatment with no control or comparison group
        • useful for generating hypotheses for additional studies
    • Evidence
      • level IV evidence
    • Example
      • you have found that several of your patients who have used a new lipid lowering medication have developed hemorrhagic cysts. You want to alert other members of the community of this possible association.
    • Orthopaedic Literature Examples 
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