Lecture Notes: Effective Vaccines and Observational Studies vs Experiments

Key Concepts

Experiments

• Definition: Involves imposing a treatment on observational units.
• Characteristics of Well-Designed Experiments:
  • Random assignment to groups.
  • At least two comparison groups.
  • Control over variables.
  • Imposition of a treatment.
• Purpose: Can often claim that explanatory variables cause response variables.

Observational Studies

• Definition: Data is collected without imposing treatments.
• Characteristics:
  • Association can be observed but causation cannot be determined.
  • More ethical in situations where imposing treatment is not possible.
• Use Cases: When experimentation is not feasible due to ethical concerns or practicality.

Ethical Considerations in Experiments

• Historical Example: WWII U.S. government experiments involving mustard gas on soldiers.
  • Conducted without informed consent.
  • Highlighted unethical practices leading to post-war guidelines for ethical experimentation.
• Modern Standards: Cannot experiment on humans or animals without informed consent and ethical oversight.

Experiment Structure (Mustard Gas Example)

• Sample: Description and division into treatment and control groups.
• Random Assignment: Use of randomization to ensure unbiased groups.
• Replication: Important to minimize the impact of anomalies or unique responses.

Observational Studies: Example with Vaccines

• COVID-19 Vaccine Study:
  • Sample: Frontline and healthcare workers.
  • Variables: Vaccine status and COVID infection.
  • Observational as no treatment was imposed by researchers.
  • Potential confounding variables include level of exposure, stress, sleep, etc.

Confounding Variables

• Definition: Variables that could influence the observed association.
• Examples:
  • Weather impacting both ice cream sales and drowning incidents.
  • Age affecting shoe size and reading ability in students.

Case Studies

• Experiment vs Observational Study:
  • Observational studies are identified by the lack of imposed treatment and the presence of passive data collection.
  • Experiments involve active manipulation and control over conditions.

Practice Scenarios

1. Shoe Size and Reading Scores

   • Observational study: No treatment imposed.
   • Confounding variable: Age impacts both shoe size and reading ability.

2. Urban vs Rural Cancer Rates

   • Observational study: Unlikely to force people into different living conditions.
   • Confounding variables: Smoking prevalence, education level, healthcare access.

Summary

• Experiments and observational studies differ mainly in treatment imposition.
• Observational studies are limited in claiming causation due to potential confounding variables.
• Ethical considerations are paramount when designing studies.

Reflection

• Be able to identify whether a study is experimental or observational.
• Understand the role of confounding variables and how they impact study conclusions.
• Recognize the ethical dimensions of conducting experiments on humans and animals.