difference between randomized experiment and observational study

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Observational Study vs Experiment with Examples

By Jim Frost 1 Comment

Comparing Observational Studies vs Experiments

Observational studies and experiments are two standard research methods for understanding the world. Both research designs collect data and use statistical analysis to understand relationships between variables. Beyond that commonality, they are vastly different and have dissimilar sets of pros and cons.

Experiments are controlled investigations where researchers actively manipulate one or more variables to observe the effect on another variable, all within a carefully controlled environment. Researchers must be able to control the treatment condition each subject experiences. Experiments typically use randomization to equalize the experimental groups at the start of the study to control potential confounders.

In this post, we’ll compare an observational study vs experiment, highlighting their definitions, strengths, and when to use them effectively. I work through an example showing how a study can use either approach to answer the same research question.

Learn more about Experimental Design: Definition and Types and Confounding Variable Bias .

Strengths of Observational Studies

Real-World Insights : Observational studies reflect real-world scenarios, providing valuable insights into how things naturally occur. Well-designed observational studies have high external validity , specifically ecological validity .

Does Not Require Randomization : Observational studies shine when researchers can’t manipulate treatment conditions or ethical constraints prevent randomization. For example, studying the long-term effects of smoking requires an observational approach because we can’t ethically assign people to smoke or abstain from smoking.

Cost-Effective : Observational studies are generally less expensive and time-consuming than experiments.

Longitudinal Research : They are well-suited for long-term studies or those tracking trends over time.

Strengths of Experiments

Causality : Experiments are the gold standard for establishing causality. By controlling variables and randomly assigning treatment conditions to participants, researchers can confidently attribute changes to the manipulated factor . Well-designed experiments have high internal validity . Learn more about Correlation vs. Causation: Understanding the Differences .

Controlled Environment : Experiments offer a controlled environment, reducing the influence of confounding variables and enhancing the reliability of results.

Replicability : Well-designed experiments are often easier to replicate, increasing researchers’ ability to compare and confirm results.

Randomization : Random assignment in experiments minimizes bias, ensuring all groups are comparable. Learn more about Random Assignment in Experiments .

When to Choose Observational Studies vs Experiments

Observational studies vs experiments are two vital tools in the statistician ’s arsenal, each offering unique advantages.

Experiments excel in establishing causality, controlling variables, and minimizing the impact of confounders. However, they are more expensive and randomly assigning subjects to the treatment groups is impossible in some settings. Learn more about Randomized Controlled Trials .

Meanwhile, observational studies provide real-world insights, are less expensive, and do not require randomization but are more susceptible to the effects of confounders. Identifying causal relationships is problematic in these studies. Learn more about Observational Studies: Definition & Examples  and Correlational Studies .

Observational studies can be prospective or retrospective studies . On the other hand, randomized experiments must be prospective studies .

The choice between an observational study vs experiment hinges on your research objectives, the context in which you’re working, available time and resources, and your ability to assign subjects to the experimental groups and control other variables.

If you’re looking for a middle ground choice between observational studies vs experiments, consider using a quasi-experimental design. These methods don’t require you to randomly assign participants to the experimental groups and still allow you to draw better causal conclusions about an intervention than an observational study. Learn more about Quasi-Experimental Design Overview & Examples .

Understanding their strengths and differences will help you make the right choice for your statistical endeavors.

Observational Study vs Experiment Example

Suppose you want to assess the health benefits of consuming a daily multivitamin. Let’s explore how an observational study vs experiment would evaluate this research question and their pros and cons.

An observational study will recruit subjects and have them record their vitamin consumption, various health outcomes, and, ideally, record confounding variables. The participants choose whether or not to take vitamins during the study based on their existing habits. Some medical measurements might occur in a lab setting, but researchers are not administering treatments (vitamins). Then, using statistical models, researchers can evaluate the relationship between vitamin consumption and health outcomes while controlling for potential confounders they measured.

An experiment will recruit subjects and then randomly assign them to the treatment group that takes daily vitamins or the control group taking a placebo . Randomization controls all confounders whether the researchers know of them or not. Finally, the researchers compare the treatment to the control group. Learn more about Control Groups in Experiments .

Most vitamin studies are observational because the randomization process would be challenging to implement, and it raises ethical concerns in this context. The random assignment process would override the participants’ preferences for taking vitamins by randomly forcing subjects to consume vitamins or placebos for decades . That’s how long it takes for the differences in health outcomes to manifest. Consequently, enforcing the rigid protocol for so long would be difficult and unethical.

For an observational study, a critical downside is that the pre-existing differences between those who do and do not take vitamins daily comprise a pretty long list of health-related habits and medical measures. Any of them can potentially explain the difference in outcomes instead of the vitamin consumption!

As you can see, using an observational study vs experiment involves many tradeoffs! Let’s close with a table that summarizes the differences.

Differences between an Observational Study and Experiment

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Reader Interactions

October 22, 2023 at 11:17 pm

Well stated: ” Both research designs collect data and use statistical analysis to understand relationships between variables” I was not familiar with the terms research designs. 😀

PS, I am already receiving all your wonderful mailing. I binge-read them every few weeks. I am planning on getting your other two books when I can. Thanks, and Cheers!

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