6.5 – EXPERIMENTAL AND OBSERVATIONAL STUDIES

Unit 6 – Data Analysis and Probability

Georgia Performance Standards

MM3D3 – Students will understand the differences between experimental and observational studies by posing questions and collecting, analyzing, and interpreting data.

Vocabulary

A study is often conducted in two groups:

Experimental group – undergoes some procedure or treatment

Control group – does not undergo the procedure or treatment.

Experiments

In a well designed experiment, everything else about the experimental group and control group is as similar as possible so that the effect of the procedure or treatment can be determined.

Studies

In an experimental study, the investigator assigns the individuals to the experimental group or the control group.

In an observational study, the assignments of individuals to the experimental group and the control group are outside of the control of the investigator.

Identify Studies

Tell whether the study is an experimental study or an observational study. Explain your reasoning.

a) You want to study the effects of regular exercise on a person’s heart rate. You measure the heart rate of a person at rest and again after jogging in place for 5 minutes. The control group is students who are not on a school athletic team. The experimental group is students who are on a school athletic team.

Identify Studies (Solution)

Tell whether the study is an experimental study or an observational study. Explain your reasoning.

a) This study is an observational study because the assignments of the individuals to the experimental group and the control group are outside of your control. The students “sort themselves” into the two groups based on their previously-made decisions about whether to participate in school sports.

Identify Studies

Tell whether the study is an experimental study or an observational study. Explain your reasoning.

b) You want to study the effects that music has on the ability to recall knowledge. Each individual in your study is given material to read on the same unfamiliar topic and then asked to take a factual quiz on the material. The control group is individuals who read the material and take the quiz in a quiet room. The experimental group is individuals who read the material and take the quiz in a room that has classical music playing.

Identify Studies (Solution)

Tell whether the study is an experimental study or an observational study. Explain your reasoning.

b) This study is an experimental study because you are assigning individuals to the control group and the experimental group.

Identifying Flaws in Experiments

A manufacturing company conducts an experiment to test how effective a new foot cushion for shoes is at relieving back pain. The experimental group consists of young college athletes who are given the foot cushions to use during athletic practices and games. The control group consists of non-athletic college students who are not given the foot cushions.

The company finds that the people in the experimental group experience less back pain than those people in the control group. As a result, the company concludes that the foot cushions are effective. Identify any flaws in this experiment, and describe how they can be corrected.

Identifying Flaws (Solutions)

College athletes are likely to be more physically active than non-athletic students. This means it could be physical activity rather than the foot cushions that explains why the experimental group had less back pain than the control group.

To correct this flaw, the manufacturing company could redesign the experiment so that the physical activity of the people in the experimental group is similar to the physical activity of the people in the control group.

Guided Practice

Page 234: 1-4 In exercises 1 and 2, tell whether the study is an

Experimental study or an observational study. Explain your reasoning.