Updated: 9/26/2020

Clinical Trial Design

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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
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 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
    • single blinded study
    • double blinded study 
    • triple blinded 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
Case-control study
Meta-analysis
Cross-sectional Study
Case Series
 

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Questions (9)
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(OBQ13.195) A study was designed to measure the benefit of subacromial corticosteroid injections. Participants were randomized to methylprednisolone acetate 40 mg with lidocaine 1% or lidocaine 1% alone. The participants were not provided with information of their treatment allocation. The subacromial injection was prepared and administered by a single orthopaedic surgeon. Results were collected by the orthopaedic surgeon using clinical and patient satisfaction outcome scores at 6, 12, and 24 weeks. Which of the following would best describe this type of study? Tested Concept

QID: 4830
1

Double blinded randomized and controlled study

4%

(170/4465)

2

Single blinded randomized study

88%

(3948/4465)

3

Retrospective study

1%

(28/4465)

4

Case-control study

2%

(88/4465)

5

Prospective cohort study

4%

(197/4465)

L 1 B

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(OBQ11.243) A clinical trial is underway for patients with wrist extensor tendinitis. One group of 100 patients are treated with short arm casting. Another group of 100 patients are treated with physical therapy. During analysis of the results, it becomes apparent that 30 patients in the physical therapy group did not complete the full course of physical therapy. Despite not completing a full course of physical therapy, these 30 patients were included in the physical therapy group for analysis. This analysis is an example of which of the following? Tested Concept

QID: 3666
1

Per-protocol

6%

(372/5941)

2

Crossover analysis

6%

(345/5941)

3

Intent-to-treat

79%

(4717/5941)

4

Bayesian analysis

5%

(278/5941)

5

Effect size

3%

(177/5941)

L 2 C

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(OBQ09.34) What is the primary purpose of utilizing a computer random number generator for patient randomization when designing a Level I therapeutic controlled trial? Tested Concept

QID: 2847
1

To increase treatment effect

0%

(2/727)

2

To prevent selection bias

97%

(705/727)

3

To generate enough power

1%

(4/727)

4

To achieve statistical significance

2%

(12/727)

5

To perform as-treated analysis

0%

(1/727)

L 1 D

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(OBQ05.86) A clinical study for lateral epicondylitis allocates 1 group to receive physical therapy for 4 weeks and another group a new oral medication for 4 weeks. Then the 2 groups immediately switch therapies with one another for the next 4 weeks. The half-life of the medication used in the study is 2 weeks. Which of the following best describes the bias that is present in this study design? Tested Concept

QID: 972
1

Recall bias

5%

(57/1131)

2

Verification bias

4%

(42/1131)

3

Washout period bias

74%

(834/1131)

4

Detection bias

8%

(85/1131)

5

Incorporation bias

10%

(109/1131)

L 2 A

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(OBQ04.149) A research study is initially designed as a high-quality randomized control trial. The study seeks to demonstrate a different clinical outcome with treatment A compared to treatment B for a specific disease. However, at the completion of the study the investigators are only able to obtain 70% follow-up of patients. What level of evidence should be assigned to this study? Tested Concept

QID: 1254
1

1

19%

(269/1437)

2

2

70%

(1004/1437)

3

3

9%

(132/1437)

4

4

2%

(26/1437)

5

5

0%

(3/1437)

L 2 C

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