Transcript Independent Variable

Fall 2013
Lecture 3 – Chapter 3
The Starting Point
Research Terminology
Variables
Variable: Any measurable aspect of behavior or
influence on behavior that may change
Or…
things you manipulate
and things you measure
Independent Variable: IV
Dependent Variable: DV
Independent Variable:
Normally (true experiment), it is the variable that
you manipulate
ANY VARIABLE THAT DEFINES SEPARATE GROUPS
…”I” do the research…it’s what “I” manipulate
Either give some subjects 100mg of a drug or give them
25mg or placebo
Here the IV is DRUG (varying doses)
So, by randomly assigning them to a drug dose you are
creating the groups (conditions) of the experiment
IV
1 mg
10 mg
Sugar pill
Either give some subjects 20, 60 or 40 watts and test
their performance on a math test
20 watts
60 watts
100 watts
Then vary the type of math test: algebra, geometry
Independent Variable:
Normally (true experiment), it is the variable that
you manipulate…but in
a quasi-experiment
not really manipulated
the IV is the preexisting condition that
the subjects brings into the experiment
(also called the “subject” or “classification” variable)
ex: sex, age, ethnicity
IV: Levels
In general, the number of levels of an independent
variable is the number of experimental conditions
Dependent Variable:
In either True experiment, Quasi-experiment, or
Correlational research:
The variable that you hypothesize to have a relationship
with the IV..that you expect to be affected by the IV
The variable that you measure
The response of your subject
Examples of Dependent Variable:
Reaction time
cancer cells
errors on memory test
Naturalistic Observation – Low constraint
No manipulation
No IV
DV? Behavior?
“Variable of interest”
Case Study – Low constraint
No manipulation
No IV
DV? Behavior?
“Variable of interest”
Correlational research – Constraint
days attended
40
30
IV? Grouping variable
DV? response
20
10
0
0 10 20 30 40 50 60 70 80 90100
percentage (class grade)
Experimental Research – highest constraint
“True Experiment”
This should be easy now!
IV? Grouping variable
DV? response
One last Variable – Not a good thing
Any variable or factor not controlled for by the
experimenter that might affect the DV
Threat to validity of experiment
Internal Validity: are we testing what we set out to
test?
Methodological soundness of experiment
examples of extraneous variables
testing subjects on a memory test
…temperature in the room is HOT …impact on
the tests results
Examining the effects of alcohol
on driving and obeying posted signs…but you don’t
assess their vision
Experimental Research – highest constraint
“True Experiment”
Research Ethics
Human Subjects Institutional Review Board (HSIRB)
- Consists of members of community & peers
- Review research proposals – Yea or Nay
- Assure that project meets ethical standards
(set by APA. NIH & institution)
Informed Consent: a form that provides the subject
with enough info to make an “informed” decision
Research Ethics
Institutional Care and Use of Animal Committee (IACUC)
Veterinarian, non scientist, scientist/researcher
Housing, care & use