3. Choosing the best study design

Study design

Learning outcomes:
Observational Studies
➔ Define cohort studies
➔ Distinguish between prospective and retrospective cohorts
➔ Explain the nested case-control design and strategy
➔ Describe the multiple-cohort design
➔ Define cross-sectional studies
➔ Explain why cross-sectional studies yield weaker evidence for causality than cohort studies
➔ Define case-control studies and their benefits and problems
➔ Describe case-crossover studies.

Randomized Blinded Trials
Define randomized blinded trials
Explain how to design RBTs
Describe how to choose the intervention and control conditions
Describe how to define outcomes and adverse effects
Describe how to select participants
Describe how to measure baseline and outcome variables
Evaluate approaches to randomizing and blinding.

Studies of medical tests

Learning outcomes:
➔ Understand the definition of studies of medical tests and how these studies differ from therapeutic intervention trials or studies to assess causality
➔ Explain how to select subjects for a study of a medical test
➔ Understand how to measure reproducibility of a test including use of kappa and the coefficient of variation
➔ Define key metrics to use in studies that assess the accuracy of a diagnostic test including sensitivity, specificity, predictive value, ROC curves, and likelihood ratios
➔ Understand how to design studies of clinical prediction rules and the associated limitations and challenges with this design.

Enhancing causal inference

Learning outcomes:
➔ Describe cause-effect relationships and enumerate the four rival explanations
➔ Identify ways to minimize chance
➔ Discuss bias and identify ways to avoid bias
➔ Identify ways to make confounding less likely
➔ Offer several suggestions or strategies for incorporating opportunistic observational designs
➔ Explain how causal inference can be enhanced by positive evidence.

The methods: matching study designs to research questions

Learning outcomes:
➔ Why the methods section is the most important part
➔ How to report study methods accurately and fully
➔ How to report methods to minimise bias and confounding
➔ How to use reporting guidelines for different study types.

Subjects and variables

Learning outcomes:
➔ Define sample and population, and describe how sample and population inform all clinical
➔ Identify criteria for a target population
➔ Compare and contrast approaches to sampling
➔ Describe several strategies for recruiting a sample of subjects.

Sample size and power

Learning outcomes:
➔ List the steps for estimating sample size for an analytic study
➔ Explain other considerations in calculating sample size for analytic studies
➔ List the steps for estimating sample size for descriptive studies
➔ Identify strategies to minimize the required sample size
➔ Explain other strategies for estimating sample size when there is insufficient information


Learning outcomes:
➔ Define and describe box models
➔ Define and describe standard error
➔ Define and describe p-values
➔ Define null hypothesis
➔ Select the appropriate statistical tests for your study.

Questionnaires and qualitative research

Learning outcomes:
➔ Describe steps an investigator can take to ensure that questionnaires and interviews are as valid and reproducible as possible
➔ Define open-ended questions and closed-ended questions and devise several examples of both types of questions
➔ Identify desirable question elements as well as pitfalls to avoid
➔ Design a one-page instrument that is easy to read, easy to understand, and suitable for data entry.

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