Transcript Political Research and Statistics

Measurement
9/6/2012
Readings
• Chapter 3 Proposing Explanations, Framing
Hypotheses, and Making Comparisons
(Pollock) (pp.48-58)
• Chapter 1 Introduction to SPSS (Pollock
Workbook)
OPPORTUNITIES TO DISCUSS
COURSE CONTENT
Office Hours For the Week
• When
– Friday 11-1
– Monday 11-1
– Tuesday 8-12
– And by appointment
Course Learning Objectives
1. Students will learn the research methods
commonly used in behavioral sciences and
will be able to interpret and explain empirical
data.
2. Students will learn the basics of research
design and be able to critically analyze the
advantages and disadvantages of different
types of design.
A Test of Scientific Knowledge
A CAUSAL HYPOTHESIS
What is a causal hypothesis?
• The Boldest Hypothesis
out there
• A relationship that will
occur 100% at all times,
no exceptions
• Difficult to Prove
To Prove a Causal Hypothesis
1. A Change in the Independent Variable will
always cause a change in the dependent
variable.
2. A change in X always precedes a change in Y
3. X is necessary and sufficient to cause a
change in Y
Causality is the heart of scientific
knowledge!
MEASUREMENT
What is Measurement
• How we quantify our concepts
• The most basic measures talks about how
much (votes, money, etc).
Good Measures
• Start with Good
Operationalization
• Are precise and
accurate
• Can actually be done
• This is difficult
Bad Measures
• Are unreliable
• Are inaccurate
• This leads to bad
conclusions
RELIABILITY AND VALIDITY
Measurement Validity
• A measure is valid if it measures what it is
supposed to measure
• The measure and the concept correspond
Operational Validity
• The measure does what it says
• This can be difficult to establish
Face Validity
• The simplest way to
seek validity
• The Measure looks
good on its face
• We ask People, use the
literature
• Problems?
Content Validity
• Using several measures
of a concept to get at
the whole concept
• Good for multidimensional concepts
(e.g. political
participation)
Trust in Government
•
•
•
•
Trust the Federal Government
Is the Government Run for the Benefit of All
Do People in Government Waste Tax Money
Are Government Officials Crooked
Freedom House Index
• 27 Questions
A. Electoral process
B. Political pluralism &
participation
C. Functioning of
government
D. Freedom of expression &
belief
E. Associational &
organizational rights
F. Rule of law
G. Personal autonomy and
individual rights
The Misery Index
Predictive Validity
• Using a measure to
predict a future
outcome
• This is very difficult in
the social sciences
The NFL Combines
• 40-yard dash
• Bench press
• Vertical jump
• Broad jump
• 3 cone drill
• Shuttle run
Newsweek from 1978
The LSAT’s
• The LSAT is designed to
measure skills that are
considered essential for
success in law school
• The LSAT is a strong
predictor of first-year
law school grades
• What doesn’t it
measure?
RELIABILITY
Measurement Reliability
• A measurement will
provide the same
results upon repeated
tests
• The more consistent the
results… the more
reliable the measure
Random Error
• Outside of the control
of the researcher
– Outlier case
– People’s feelings
– weather
• Large sample sizes
reduce this
Bad Weather and Turnout
Non-Random Error
• Systemic Researcher
Error
–
–
–
–
–
Poor design
Lazy administration
Intentional error
Small samples
carelessness
• This will distort the
measure of a concept
Non-Random Error
Ensuring Reliability
• Good Definitions and unambiguous questions
• Clear Directions
• Making results and information available to
other researchers
Methods for ensuring Reliability
• Alternative forms technique
• Test-Retest
A measure can be reliable without
being valid, but a measure cannot
be valid without being reliable!
A way of getting content validity
INDEXES AND SCALES
Why create a scale/index?
• To form a composite
measure of a complex
phenomenon by using
two or more items
• Get at all facets
• Simplify our data
Examples
• GPA
Likert Scale
• A common way of
creating a scale
• Advantages
• Disadvantages
Guttman Scaling
• Employs a series of items to produce a score
for respondents
• Ordering questions that become harder to
agree with
• Advantages and disadvantages
Guttman Scale