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SPEC Course Research Guide

 What are the differences between scientific studies?


Some scientific articles are considered to be of a higher quality than others. 

Scientific studies have different designs characterized by different types of methodologies.

These study designs can be placed in a hierarchy, called the evidence pyramid. The highest quality evidence is located at the top of the pyramid and the lowest quality evidence is located at the bottom.



Definitions of Study Designs

For your progress report, you will need to identify the type of study you have found. For more information on the different types of study designs, click here

Look at the Methods section of your study's abstract to determine the study design. 

Here are summaries of the different types of study designs:

randomized controlled trial is an experiment conducted using two groups: a control and an intervention
group. The intervention is given a treatment for a disease, while the control group is given a different treatment or no treatment at all. 

Example: Testing a binocular iPad game versus patching for the treatment of amblyopia to see which treatment is more effective


cohort study looks forward in time (meaning it is prospective). It examines a population that does not have a disease over a period of time to see who develops that disease. It looks at an exposure (like, saying, smoking) and tries to trace it to an outcome (lung cancer). 

Example: A group of Medicare beneficiaries with a diagnosis of cataracts were analyzed from 2002 to 2012. Surgery for cataracts decreased mortality incidence.


case-control study looks backward in time (meaning it is retrospective). This type of study looks at a group of patients with a disease and matches them to a group of patients without a disease (the control group) to try and identify exposures and outcomes.

Example: Researchers look through the medical records of a group of patients with lung cancer to figure out how many participants were smokers. 

cross-sectional study looks at a group of diseased and non-diseased people at one point in time or over a short period of time. It usually measures the prevalence of a disease, typically by administering a survey.

Example: Researchers surveyed 16 ophthalmology departments of hospitals, asking 220 patients with allergic conjunctivitis about their comorbidities and the time and length of their allergy episodes.

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