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A number of different study designs are indicated below.

Contents 1 Treatment studies 2 Observational studies 3 Important considerations 4 Other terms 5 See also 6 External links

[edit] Treatment studies

• Randomized controlled trial
  • Double-blind randomized trial
  • Single-blind randomized trial
  • Non-blind trial
• Nonrandomized trial (quasi-experiment)
  • Interrupted time series design (measures on a sample or a series of samples from the same population are obtained several times before and after a manipulated event or a naturally occurring event) - considered a type of quasi-experiment

[edit] Observational studies

• Cohort study
  • Prospective cohort
  • Retrospective cohort
  • Time series study
• Case-control study
  • Nested case-control study
• Cross-sectional study
  • Community survey (a type of cross-sectional study)

[edit] Important considerations

When choosing a study design, many factors must be taken into account. Different types of studies are subject to different types of bias. For example, recall bias is likely to occur in cross-sectional or case-control studies where subjects are asked to recall exposure to risk factors. Subjects with the relevant condition (e.g. breast cancer) may be more likely to recall the relevant exposures that they had undergone (e.g. hormone replacement therapy) than subjects who don't have the condition.

The ecological fallacy may occur when conclusions about individuals are drawn from analyses conducted on grouped data. The nature of this type of analysis tends to overestimate the degree of association between variables.

[edit] Other terms

• The term retrospective study is sometimes used as another term for a case-control study.
• Superiority trials are designed to demonstrate that one treatment is more effective than another.
• Non-inferiority trials are designed to demonstrate that a treatment is at least not appreciably worse than another.
• Equivalence trials are designed to demonstrate that one treatment is as effective as another.
• When using "parallel groups", each patient receives one treatment; in a "crossover study", each patient receives several treatments.
• A longitudinal study research subjects over two or more points in time; by contrast, while a cross-sectional study assesses research subjects at one point in time.

[edit] See also

• Epidemiological methods
• Clinical trial
• Meta-analysis
• Design of experiments
• Experimental control

[edit] External links

• Epidemiologic.org Epidemiologic Inquiry online weblog for epidemiology researchers
• Epidemiology Forum An epidemiology discussion and forum community to foster debates and collaborations in epidemiology
• Some aspects of study design Tufts University web site
• Comparison of strength Description of study designs from the National Cancer Institute
• Political Science Research Design Handbook Truman State University website

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