1. Understanding Experimental Research:
Independent and Dependent variables

2. Experiment1
Hypothesis: Taking tests in hot rooms decreases test scores.
Students are randomly assigned to take a test in either a hot room or a comfortable room. Test scores will be compared to see if hot rooms negatively affect test-taking.
What is the independent variable? What is the Dependent Variable?
Students
Room temperature
Test scores
Tests
How would we design this experiment with operational definitions of the variables?
Students frequently try to make the participants in studies the independent or dependent variable.

3. Experiment 2
Hypothesis: Newborns gaze longer at a drawing of a face-like image than at a bull’s-eye pattern.
Newborns are shown, in random order, the stimuli: A face-like image, a bull’s-eye pattern, and a blank screen. Each newborn is timed to see how long they look at each.
What is the independent variable? What is the dependent variable?
Random order
Length of gaze
The stimuli
Newborns
How is this an example of a “within-subjects” design? How could you design it so that it is a “between-subjects” design?
This hypothesis was taken from the chapter 5 fact or falsehood handout. For this experiment, ask students why the images need to be presented in random order.

4. Experiment 3
Hypothesis: Without their sense of smell, it may be difficult to distinguish a cold cup of coffee from a glass of red wine.
Participants are blindfolded and their noses are pinched closed. They are then presented with a cold cup of coffee, a cup of red wine, and a cup of water, in random order. Each is presented 3 times. Participants are asked to sip each one, guessing the contents of the cup. Next the participants, still blindfolded but with unpinched noses, taste the contents of each cup again, again guessing each cup’s contents.
What is the independent variable? What is the dependent variable?
Being able to smell or not
Participants
The contents of each cup
Identifying the contents of each cup
Being blind-folded
What concept is illustrated by the fact that the participants were blind-folded?
This hypothesis was taken from the chapter 6 fact or falsehood handout. For this experiment, ask students why the participants were blindfolded.

5. Experiment 4
Hypothesis: Televised violence leads to aggressive behavior by teenagers who watch the programs.
Teenagers ages are randomly assigned to watch either a violent movie or an equally engaging but non-violent movie. Afterwards while playing a game, they are given an opportunity to punish their competitor by blasting a loud sound in their competitor’s headphones. The teenage participants get to choose how long to administer the sound.
What is the independent variable? What is the dependent variable?
The competitor
Type of movie
Length of the loud sound
Teenage participants
Why is random assignment necessary?
This hypothesis was taken from the chapter 7 fact or falsehood handout. For this experiment discuss the role of deception. The study would be designed so that the teenagers thought they were participating in 2 separate studies. Following the movies, the participants may be given a bogus questionnaire so that they’d think the study was over and that they were moving on to a second study on competition, say. You may also want to discuss confounding variables here. Why did the control group movie need to be equally engaging?

6. Experiment 5
Hypothesis: When people learn something while intoxicated, they recall it best when they are again intoxicated.
Participants are given enough alcohol to become intoxicated, and then they watch a 30-minute instructional video. The next day the participants are randomly divided into two groups. One group is again given the same amount of alcohol as they had the previous day. The other group is given a glass of water with a little vodka around the rim. Both groups are given a test on the material covered in the video.
What is the independent variable? What is the dependent variable?
Alcohol
Intoxication
Test scores
Instructional video
What is the role of a placebo in this experiment? How might it be an even stronger experiment?
This hypothesis was taken from the chapter 8 fact or falsehood handout. For this experiment you may want to discuss the role of placebos and the importance of controlling for placebo effects, in this case by making the non-alcohol group think they were getting alcohol.