Skill 3

Skill Goal: Determine if a study is observational or an experiment

• An observational study observes individuals and measures variables of interest but does NOT attempt to influence the responses. The purpose of an observational study os to describe a group or situation.
• An experiment deliberately imposes some treatment on individuals in order to observe their responses. The purpose of an experiment is to study whether the treatment causes a change in the response.

Practice Problems

1. One study of cell phones and the risk of brain cancer looked at a group of 469 people who have brain cancer. The investigators matched each cancer patient with a person of the same sex, age, and race who did not have brain cancer, then asked about cell phones. Result: "Our data suggest that use of hand-held cellular phones is not associated with risk of brain cancer."

a) Is this an observational study or an experiment? Why?

b) What individuals are measured, and what variables are recorded?

2. My grandmother once told me that the color red makes bees angry. Here's a method I've designed to test her claim. I'll select half of my students (by drawing names from a hat) to wear re clothes and the other half to wear white clothes. Then I'll turn a bunch of bees loose in our classroom and see how many times each student is stung.

a) Is this an observational study or an experiment? Why?

b) If students wearing red clothes are stung much more often than students wearing white, can we conclude that the color causes bees to sting more? Why or why not?

3. Is there a relationship between physical fitness and leadership ability? To answer this question, researchers recruited 100 students who are willing to take part in an exercise program. The volunteers are divided into a low-fitnes group on the basis of a physical examination. All students then take a test designed to measure leadership, and the results for the two are compared.

a) Is this an experiment or an observational study? Explain your answer.

Answers

1. a) This study is an observational study because nothing was done to the cancer patients that influenced the results of the study. The cancer patients were just matched with non- cancer patients and asked a series of questions.

b)Cancer Patients and Non-Cancer Patients are the individuals being measured. Their usage of cell phones is the variable.

2. a) This is an experiment because each student was assigned a specific color to wear.

b) Yes we could conclude that based on the grandma's claim or we could disagree based on the fact that other things could aggravate a bee making it sting a student.

3. This is an observational study because no treatment was imposed on the two groups.

Main difference between the an observational study and an experiment: In order for a study to be experimental you have to DO SOMETHING or MANIPULATE the individual otherwise it is observational.

CONGRATULATIONS! Margot, I have chosen you to do then next blog!