Definitions, Scaling, Graphs
-- something that can take on more than one value. Syn. - fluctuates, changes,
dynamic. Ant. - constant, fixed, unchanging.
Examples of variables
Some possible values
Blue, Brown, Green
Freshman, Sophomore, Junior, Senior
6, 19, 25, 55, 70 (years)
60, 65, 72, 84 (inches)
97, 101, 159, 220 (lbs.)
Visualization (speed of rotation)
1.5, 2.0, 2.5, 3.0 (seconds)
500, 600, 750 (scale scores)
Curiosity (personality scale)
40, 50 ,60 (scale scores)
Independent variable (IV)
- that which explains or causes; usually manipulated (cause).
Dependent variable (DV)
- that which is explained or is influenced (effect).
Examples of IVs & DVs
Student volunteers given a "study drug."
Half get mild dose of caffeine, half get
saline (nobody knows which is which).
Both take exam the next day.
IV - type of drug; DV -exam score.
Want to know whether using a microcomputer simulation can help train pilots to
better communicate when they fly.
Half the pilots are given flight training with the
The other half play video games (Asteroids) with the same
microcomputer for the same amount of time.
All pilot then fly full motion simulator
through same series of problems.
Instructor pilots (blind to condition) evaluate all with
IV=training type; DV=evaluation of flight in full motion sim.
Want to know whether SAT scores predict grades in college.
Collect SAT scores
from entering freshmen.
Collect GPAs at end of year.
Look for association.
IV=SAT; DV = GPA.
Continuous vs. Discrete Variables
In statistics and mathematics (Thorne & Slane), continuous variables correspond to real
numbers and discrete variables correspond to integers.
Real numbers take on an infinite
number of values; integers only take whole number values.
Number of Siblings
Number of errors on a test
Number of bar presses
In math/stat, there is an enormous difference between continuous and discrete variables.
This distinction is virtually never important in psychology.