4.2a Observational Study versus Experiment

All 200 fifth grades at a school are randomly assigned to one of two groups. One group studies addition of fractions with the aid of a calculator, the other studies the same topic without a calculator. Scores on a fractions test are compared after two weeks.

A researcher stood at a school parking lot entrance to see if the color of a car is related to the driver not wearing a seatbelt.

A professor finds that people who are obese have higher cholesterol levels than those who are not obese.

A researcher is interested in learning how people use the neighborhood park. The researcher goes to the park daily for a month and records how many people are on the playground, how many are on the basketball court, how many are at the picnic tables, and how many are at the skate park. What type of study is this?

A researcher is interested in how caffeine affects sleep. He has 100 people spend the night in the lab. Before bed, he gives 50 people decaffeinated coffee and 50 people caffeinated coffee. He records the brain waves of each participant throughout the night. What kind of study is this?

Which of the following is a key distinction between well designed experiments and observational studies?

Does lack of sleep affect your academic performance? A student explores this question by asking everyone in his statistics class to write down on a piece of paper his or her score on a recent test and a total number of hours of sleep he or she got on the last three nights before taking the test.

A football coach thinks lessons in yoga will improve the flexibility of his players and thereby reduce injuries. To test his theory, he randomly divides the players on the team into two groups. One group has 45 minutes of yoga training each day. The players in the other group do the standard stretching routine the team has used in the past. He compares flexibility in the two groups at the end.

To test the effect of music on productivity, a group of assembly line workers are given portable MP3 players to play whatever music they choose while working for one month. For another month, they work without music. The order of the two treatments for each worker is determined randomly.