In the previous in-class activity, you learned about a type of statistical study known as an experimental study. However, it is not always appropriate to use experimental studies.

1) Can you think of a situation in which collecting data to answer a question is more appropriate because an experiment would not be appropriate?

Collecting data is more important for unethical things, biased outcomes, and limitations on design. Anything inhumane. You’re not observing results of a treatment.

In March 2020, COVID-19 was declared a pandemic by the World Health Organization. In December 2020, vaccines using Messenger RNA technology were given emergency use authorization by the Food and Drug Administration in the United States. Over the next 13 weeks, 3,950 health care personnel, first responders, and other essential and frontline workers who had received the vaccine completed weekly COVID-19 testing to determine whether they had tested positive for COVID-19. In this study, researchers were following the effectiveness of the vaccines in a real-world setting.

2) Come up with at least two reasons that this was an observational study.

There were treatments and they observed the results.

3) Identify at least one potentially confounding variable in this study.

A confounding variable could be that they already had covid.

4) What are some differences between an experimental study and an observational study?

Observational Study - 1 group, nothing changing, just observing data, harder to draw cause and effect, out in the real world

Experimental Study - 2 groups, controlled, changing 1 factor of interest, less likely to have confounding variables, takes place in labs

5) A PhD student collects data at a local elementary school. For each student, she records their age, grade, height, weight, shoe size, GPA, and score on a state-wide reading test for elementary school-aged children.

Part A: Is this an experimental or observational study?

Observational, only 1 group (all elementary school students)

Part B: The PhD student observes that students with larger shoe sizes tend to score higher on the state-wide reading test. She concludes that having bigger feet improves reading ability. Can you explain why her reasoning is likely to be incorrect? Can you think of another explanation for the higher test scores?

More of a generalized thing. Bigger shoe size = older in age

6) A study finds that people living in high-density urban areas develop fatal lung cancer at lower rates than people living in low-density rural areas.

Part A: Is this an experimental or observational study?

Observational, 2 groups but no treatment

Part B: A student reads this study and determines that living near many people prevents cancer. Can you think of other things that might explain why low- density areas see higher rates of lung cancer?

Less people = less chance4 to get sickness