Independent and Dependent Variables
Practice
An independent variable is a factor that is manipulated in an experiment. The experimenter
controls whether or not subjects are exposed to the independent variable. The dependent
variable is measured to determine if the manipulation of the independent variable had any effect.
For example, to test a hypothesis that eating carrots improves vision, the experimenter would
manipulate whether or not subjects ate carrots. Thus, eating carrots is the independent variable.
Each subject’s vision would be tested to see if carrot eating had any effect. Thus, vision is the
dependent variable. The subjects assigned to eat carrots are in the experimental group, whereas
subjects not eating carrots are in the control group.
Identify the independent variable, dependent variable, experimental and control groups in the
following studies.
1. A group of college students were given a short course in speed-reading. The instructor was curious if
a monetary incentive would influence performance on a reading test taken at the end of the course.
Half the students were offered $5 for obtaining a certain level of performance on the test, the other
half were not offered money.
Independent variable:
Dependent variable:
Experimental group:
Control group:
2. A social psychologist thinks that people are more likely to conform to a large crowd than to a single
person. To test this hypothesis, the social psychologist had either one person or five persons stand on
a busy walking path on campus and look up. The psychologist stood nearby and counted the number
of people passing by who also looked up.
Independent variable:
Dependent variable:
Experimental group:
Control group:
3. To test a new voice feature in a cockpit design a flight simulator was used. The simulator was
programmed to give visual readings of flight information, or to give visual and auditory (voice)
readings of flight information. All test pilots were put through a simulated emergency landing
procedure, but were randomly assigned to the visual, or visual and auditory conditions. Flight experts
rated each pilot’s performance in the simulator on a scale of 1 (very poor) to 10 (excellent).
Independent variable:
Dependent variable:
Experimental group:
Control group:
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Independent and Dependent Variables
Practice
Answers:
1. A group of college students were given a short course in speed-reading. The instructor was curious if a
monetary incentive would influence performance on a reading test taken at the end of the course. Half the
students were offered $5 for obtaining a certain level of performance on the test, the other half were not
offered money.
Independent variable: Monetary incentive ($5 or no money)
Dependent variable: Performance on reading test
Experimental group: $5 group (receive monetary incentive)
Control group: $0 group (no monetary incentive)
2. A social psychologist thinks that people are more likely to conform to a large crowd than to a single
person. To test this hypothesis, the social psychologist had either one person or five persons stand on a
busy walking path on campus and look up. The psychologist stood nearby and counted the number of
people passing by who also looked up.
Independent variable: Size of group (5 people or 1 person)
Dependent variable: Conformity (measured by number of people looking up)
Experimental group: People passing 5 person group
Control group: People passing single person. (This group gets “less” of the independent variable)
3. To test a new voice feature in a cockpit design a flight simulator was used. The simulator was
programmed to give visual readings of flight information, or to give visual and auditory (voice) readings
of flight information. All test pilots were put through a simulated emergency landing procedure, but were
randomly assigned to the visual, or visual and auditory conditions. Flight experts rated each pilot’s
performance in the simulator on a scale of 1 (very poor) to 10 (excellent).
Independent variable: Presence or absence of auditory (voice) readings. (All pilots received visual
readings, so that is a constant variable.)
Dependent variable: Ratings of pilots’ performance
Experimental group: Pilots in auditory readings condition (visual + auditory)
Control group: Pilots in visual reading only condition (no auditory)
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Independent and Dependent Variables
Practice
Dependent / Independent Variable Examples
Example 1
Dr. Imanut wants to examine whether a new drug increases the maze running performance of
older rats. Just like aging humans, older rats show signs of poorer memory for new things. Dr.
Imanut teaches two groups of older rats to find a piece of tasty rat chow in the maze. One group
of rats is given the new drug while they are learning the maze. The second group is not given the
drug. One week after having learned the maze he retests the rats and records how long it takes
them to find the rat chow.
What is the independent variable? ____
Hint: What did the researcher manipulate (allow to vary) in this study?
What is the dependent variable? ____
Hint: What was the measure of the research subjects' responses?
a) age of the rats.
b) type of maze.
c) length of time it took the rats to run the maze.
d) presence or absence of the new drug.
Example 2
A researcher wanted to study the effects of sleep deprivation on physical coordination. The
researcher selected 25 year-old male college students and deprived some of the subjects to either
24, 36, or 45 hours of sleep.
In the present study the independent variable was: ____
In the present study the dependent variable was: ____
a) the length of time the subjects were deprived of sleep.
b) the age of the subjects.
c) the gender of the subjects.
d) the physical coordination skills of the subjects.
Example 3
A researcher wanted to know whether the number of people present would influence subjects'
judgments on a simple perceptual task. In each case the other members of the group gave an
incorrect answer. The researcher then noted whether the subject conformed to the group
decision.
In the present study the independent variable was: ____
In the present study the dependent variable was: ____
a) the number of people in the group.
b) whether the group members gave the correct or incorrect answer.
c) whether the subjects conformed with the group.
d) the type of perceptual task.
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