Transcript Types of Inferential Statistics

Research Design & Analysis 1:
Class 5
• Announcements (reminders)
– lab due dates
– new lab section
– S.M.I.L.E.
• Review: non-experimental research
methods
• Introduction to experimental
methods
• Validity
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
1
New Lab Section
We have added a new section PSYC2010
LC1
Thursday 3:00-4:30: HSH 016
S.M.I.L.E. ORIENTATION MEETING
Thursday, Sept. 23rd, 6:00 p.m. BAC 244
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
2
Characteristics of nonexperimental research
• Observe but don’t manipulate
• Lack of control over extraneous
variables
Terminology
Extraneous variables: not directly
interested in but which might influence
the results of your study (these
uncontrolled variables are potential
confounded variables)
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
3
Types of non-experimental
research
• Observational research
– naturalistic observation
– participant observation
– content analysis
• Archival research
• Survey research
– questionnaires (written)
– interviews (oral)
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
4
Dreamworlds II
Sut Jhally U.M. Amherst
Exerps..
• Content analysis
– e.g. percentage of videos produced by
men
• Survey results
– consequences - survey results about
rape etc.
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
5
What you can determine/learn
• Co-occurrence of variables
– correlation
• Ability to make predictions
– regression
– predict criterion variable from
predictor variable
• Causality still unknown
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
6
Why use these designs?
• Can be useful in early stages of a
research program
• Interested in relation among variables
in the “real world”
• Only interested in predicting behaviour
(vs. understanding causal relations)
• Experimental methods not possible
– Organismic variables (you can’t assign)
– Ethics
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
7
Introduction to scientific
methods: Experimental research
• Experimentation Involves manipulation
of variables
• Experimentation involves control over
extraneous variables
– Holding extraneous variables constant
– Randomizing effects of extraneous variables
• Quasi-experimental (Ex-post-facto)
designs
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
8
Randomness?
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
9
Randomness?
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
10
Randomness
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
11
Introduction to experimental research
• Manipulation of variables
– dependent variable(s) DV
– independent variable(s) IV, levels of treatment
– control variable(s)
• Control over extraneous variables
– Holding extraneous variables constant
– Randomizing effects of extraneous variables
• Confounded variables
– covary (correlate) with the IV
• Quasi-experimental (Ex-post-facto) designs
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
12
Characteristics of a scientific
experiment
• Manipulation (of the independent
variable)
• Control (over extraneous variables)
also
• Measurement [of the dependent
variable(s)]
• Comparison [of the measurement(s)
with appropriate statistic(s)]
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
13
Experimental approach is preferred if
interested in causality
Example: Joseph Goldberg and Pellagra
– Spartanberg S.C.
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
14
Strengths and limitations of
experimental approach
• Strength is in determining causal
relations
but
• Limited applicability
– (organismic variables, ethics)
• Tight control limits generalizability
(external validity)
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
15
Internal & external validity
Internal validity: the ability of your
research design to adequately test your
hypothesis
• threatened to the extent that extraneous
variables can provide alternative
explanations (rival hypotheses) for findings
• confounded variables (can occur in both
experimental and correlational designs)
• minimize threats with careful design
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
16
Internal & external validity
External validity: the degree to which
the results of your research can be
extended beyond the research setting
and sample used.
• More an issue with applied than basic
research
• e.g., Stress and cancer study ...
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
17
Stress and Cancer
93 lab rats randomly assigned from a defined population
Random
Random
Random
assignment 31 rats assignment 31 rats assignment 31 rats
Escapable shock
Inescapable
No shock
treatment
shock treatment
treatment
Ad lib food & water Ad lib food & water Ad lib food & water
14-10 LD cycle
14-10 LD cycle
14-10 LD cycle
Percent tumour
rejection 63%
Percent tumour
rejection 27%
Percent tumour
rejection 54%
Based on Visintainer, Volpicelli, & Seligman, 1982
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
18
Results
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
19
Factors influencing external validity
• Population sampled
– “subject selection”
• Operational definitions
– “experimental arrangements”
• Parameter values
– “experimental arrangements”
• Demand characteristics
– “reactive testing”
• “Multiple-treatment interference”
from table 3-2
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
20
Internal & external validity
• Tends to be a trade off between these.
• Steps taken to enhance one type of
validity will decrease the other.
• Decide which is more important for your
study.
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
21
Research settings
• Laboratory (any artificial setting)
– simulations
– realism (mundane and experimental)
• Field (setting where behaviour
normally occurs)
• Field experiment example
– Piliavin & Piliavin, (‘72) - helping
7/17/2015
Psyc2013 Class #5 (c) Peter McLeod
22