Experiments vs. Observational Studies

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

• More subjects are available for experiments than for observational studies.

• Ethical constraints prevent large-scale observational studies.

• Experiments are less costly to conduct than observational studies.

• An experiment can show a direct cause-and-effect relationship, whereas an observational study cannot.

• Tests of significance cannot be used on data collected from an observational study.

Tags

CCSS.HSS.IC.B.3

CCSS.HSS.ID.C.9

Factors that cause differences between the experimental group and control group other than the independent variable. 

• control group
• population
• confounding variables

A psychological or physical treatment given to the control group that resembles the treatment given to the experimental group, but that contains no active ingredient. 

• independent variable
• placebo
• dependent variable

Roshanda was curious if students in her class would complete a maze faster if fast-paced music was playing in the background. She randomly assigned each student in her class to one of three groups: fast-paced music, slow-paced music, or no music. She timed each student as they individually completed a maze with their corresponding music (or no music) in the background. Students who worked with the fast-paced music, on average, completed the maze significantly faster than students in the other groups.

Can we concluded that the fast-paced music caused her classmates to finish the maze faster? Why?

• Yes, because the study included each student in her class.

• Yes, because the students were randomly selected

• Yes, because the students were randomly assigned to treatment and control groups

• Not necessarily, because the sample size was too small

Researchers were interested in the relationship between farmers’ approach to their cows and the cows’ milk yield. After surveying a random sample of 120 farmers, the researchers found that on farms where cows were called by name, milk yield was 258 liters higher on average than on farms where this was not the case.

Can we conclude that calling the cows by name caused the cows to produce more milk? Why?

• Yes, because the sample size was large

• Yes, because the farmers were randomly selected

• Not necessarily, because the sample size was too small

• Not necessarily, because this wasn't an experiment