Lecture 3 – Chapter 3

The Starting Point

Research TerminologyVariables

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

Sugar pill

IV

10 mg

1 mg

Either give some subjects 20, 60 or 40 watts and test their performance on a math test

60 watts20 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

The observation of subjects in their natural environmentThe researcher imposes no limits or changes in the environment or behavior of the subjects

No manipulation

No IV

DV? Behavior?

“Variable of interest”

Case Study – Low constraint

The subject is in a moderately limiting environmentThe researcher intervenes only slightlyAn in-depth description of one subject, organization or event

ex: medical field: Case of H.M.

No manipulation

No IVDV? Behavior?

“Variable of interest”

Correlational research – Constraint

Quantify the degree of relationship between two variableMeasurement procedure must be carefully defined and precisely followedNo manipulation of variables – two sets of measurements in the same subject then correlate

0 10 20 30 40 50 60 70 80 901000

10

20

30

40

percentage (class grade)

days

att

ende

d

IV? Grouping variable DV? response

Experimental Research – highest constraint“True Experiment”

ex: want to investigate the effects of a drug on depression

This should be easy now!IV? Grouping variable

DV? response

One last Variable – Not a good thing

Extraneous VariableExtraneous: coming from outside,

foreign, not permanent, irrelevant

Any variable or factor not controlled for by the experimenter that might affect the DV

Threat to validity of experimentInternal Validity: are we testing what we set out to

test?Methodological soundness of experiment

testing subjects on a memory test …temperature in the room is HOT …impact on

the tests results

Examining the effects of alcoholon driving and obeying posted signs…but you don’t assess their vision

examples of extraneous variables

Experimental Research – highest constraint“True Experiment”

Control: Systematic methods

reduce threats to validity

Extraneous variables (confounds)

without bias assign Subs to groups RANDOM ASSIGNMENT the setting is ALL about control

measurement procedures carefully designed and precisely followed

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

Institutional Care and Use of Animal Committee (IACUC)

Research Ethics

Veterinarian, non scientist, scientist/researcher

Housing, care & use