This document discusses key terminology used in research, including independent variables (IV), dependent variables (DV), and extraneous variables. It defines an IV as the variable that is manipulated in an experiment (e.g. drug dose) and a DV as the variable that is measured and expected to relate to the IV (e.g. reaction time). Extraneous variables are uncontrolled factors that could influence results (e.g. temperature). The document contrasts experimental, quasi-experimental, correlational, and observational research designs based on whether they involve manipulation of an IV. It also briefly discusses research ethics requirements like informed consent and review boards.

1. Fall 2013
Lecture 3 – Chapter 3
The Starting Point

2. 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

3. 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

4. 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
Sugar pill
IV
10 mg
1 mg

5. Either give some subjects 20, 60 or 40 watts and test
their performance on a math test
60 watts
20 watts 100 watts
Then vary the type of math test: algebra, geometry

6. 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

7. IV: Levels
In general, the number of levels of an independent
variable is the number of experimental conditions

8. 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

9. Examples of Dependent Variable:
Reaction time
cancer cells
errors on memory test

10. Naturalistic Observation – Low constraint
No manipulation
No IV
DV? Behavior?
“Variable of interest”

11. Case Study – Low constraint
No manipulation
No IV
DV? Behavior?
“Variable of interest”

12. Correlational research – Constraint
0 10 20 30 40 50 60 70 80 90100
0
10
20
30
40
percentage (class grade)
days
attended
IV? Grouping variable
DV? response

13. Experimental Research – highest constraint
“True Experiment”
This should be easy now!
IV? Grouping variable
DV? response

14. 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

15. 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
examples of extraneous variables

16. Experimental Research – highest constraint
“True Experiment”

17. 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

18. Institutional Care and Use of Animal Committee (IACUC)
Research Ethics
Veterinarian, non scientist, scientist/researcher
Housing, care & use