Independent and Dependent Variables 

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. (The answers are at the end of the page – scroll down to find them.)

 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:

 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)