Skip to Content

Is the Data Dirty or Clean?

The Role of Experimental Design in Human Health Studies


Chantilly A. Apollon
School of Medicine
University of California, San Francisco


This case study challenges students to differentiate between anecdotal evidence and science-based evidence related to human health. The case uses a "flipped" approach in which students watch two preparatory videos prior to attending class. The first video defines anecdotal evidence while the second characterizes the different categories of scientific studies that generate evidence that is not anecdotal. Students watch the videos, analyze scenarios for anecdotal evidence, and think about what types of evidence they use to make health-related decisions. When students meet in class, they work in groups to compare and contrast these different categories of scientific studies and classify actual research studies aided by a dichotomous key for distinguishing between different types of studies related to human health. Primarily designed for students in introductory general biology courses, the activity could also be useful for lower division nutrition, physiology, or non-major biology courses or any course where students need to differentiate between science and pseudoscience.


  • Identify differences between pseudoscience and scientific evidence.
  • Classify experimental design approaches in studies involving human health.
  • Evaluate the credibility of evidence from various types of human studies.


clinical trial; human subjects; epidemiological studies; scientific method; intervention; observation; correlation vs. causation; placebo; pseudoscience; anecdotal evidence; evidence-based medicine

Topical Areas

Scientific method, Pseudoscience

Educational Level

High school, Undergraduate lower division, Undergraduate upper division, General public & informal education



Type / Methods

Discussion, Flipped, Jig-Saw



Subject Headings

Biology (General)  |   Medicine (General)  |   Public Health  |   Statistics  |   Nutrition  |   Science (General)  |  

Date Posted


Teaching Notes

Case teaching notes are password-protected and access to them is limited to paid subscribed instructors. To become a paid subscriber, begin the process by registering.

Teaching notes are intended to help teachers select and adopt a case. They typically include a summary of the case, teaching objectives, information about the intended audience, details about how the case may be taught, and a list of references and resources.

Answer Key

Answer keys for the cases in our collection are password-protected and access to them is limited to paid subscribed instructors. To become a paid subscriber, begin the process by registering.


The following video(s) are recommended for use in association with this case study.

  • What is Pseudoscience?
    This video introduces pseudoscience as a science mimic that lacks empirical facts and procedures. The birth of Spiritualism from the Fox sisters’ hoax is briefly described. Running time: 3:53 min. Produced by Objective: Change the World, 2015.
  • Anecdotes
    This video gives an overwiew of the distinction between “clean” and “dirty” data and argues that the plural of “anecdote” is not “data.” The narrator examines various scenarios involving Reiki healing to highlight the risks associated with anecdotal evidence as it relates to health decisions. Running time: 7:42 min. Produced by Body of Evidence, 2016.
  • Categories of Experimental Design Applicable to Human Health
    Not all evidence is equal; there are differences in validity, credibility, and the ability to make direct applications to human health. Some of these differences come from the way data is collected or experimental design. This video identifies the main categories of experimental design that apply to human health. Running time: 6:32 min. Created by Chantilly A. Apollon for the National Center for Case Study Teaching in Science, 2017.