Transcript File - collingwoodresearch

POSC 202A: Lecture 1
Introductions
Syllabus
R
Homework #1: Get R installed on your laptop;
read chapters 1-2 in Daalgard, 1 in Zuur, See
syllabus for Moore and McCabe
Today: why statistics? Where is the science?
Why Statistics?
Statistics: Uncertainty
The world is stochastic, not deterministic.
Stochastic
A process characterized by chance,
randomness or probability.
In other words…
Stochastic
In other words….
SHIT HAPPENS!
Deterministic
A theory holding that, in nature, social
phenomena are causally determined by
preceding events.
Statistics: Uncertainty
Deterministic World View
Stochastic World View
Statistics: Uncertainty
Deterministic World View
Stochastic World View
The relationship between the cigarettes and death
rate (i.e. the slope) is identical in both graphs.
Statistics: Uncertainty
The world is stochastic, not deterministic.
Statistics provides a framework that allows
us to account for this uncertainty.
Statistics: Uncertainty
The world is stochastic, not deterministic.
Statistics provides a framework that allows
us to account for this uncertainty.
Statistics is about guessing, or drawing
inference.
Statistics: Uncertainty
Statistics provides a framework that allows us to
account for this uncertainty.
Statistics is about guessing, or drawing inference.
But
There are many ways to guess:
Statistics: Uncertainty
Statistics provides a framework that allows
us to explicitly account for uncertainty.
We can estimate how confident we should
be in our guesses.
Political Science
Where is the science?
Political Science
Where is the science?
What make the study of politics
scientific?
Political ScienceEmpirical study of the political world:
the study of what is, not what should be.
What do political scientists
do?
Describe, classify and explain events
relating to the political world.
What do political scientists
do?
Describe, classify and explain events relating
to the political world.
Try to distinguish the systematic from the nonsystematic.
What do political scientists
do?
Describe, classify and explain events relating
to the political world.
More specifically
We try to draw inference from what we see to
what we do not.
What is Inference?
Inference
• Making statements about what we do
not see from what we do see.
Examples?
How?
Develop and test hypotheses based on
theory.
Hypothesis
a relational statement between two or more
variables that is theoretically plausible and
empirically verifiable.
How?
Develop and test hypotheses based on
theory.
What is Theory?
Explanations for how the world works
based on experience and observation.
How?
Develop and test hypotheses based on
theory.
How do we test theories and
hypotheses?
How do we test theories and
hypotheses?
For each hypothesis we make a list of all
of the implications we can think of.
Implication
Implication
Some event or occurrence that
must be true if the theory is true.
Hypothesis testing: the mechanics
1.
2.
3.
4.
Hypothesis testing: the mechanics
1. Articulate a hypothesis
2.
3.
4.
Hypothesis testing: the mechanics
1. Articulate a hypothesis
2. Identify its implications
•
•
3.
4.
Make a list of all the things that must be true
if the theory is true.
As many as we can think of!
Hypothesis testing: the mechanics
1. Articulate a hypothesis
2. Identify its implications
3. Attempt to prove the implications
stemming from theory false.
4.
Hypothesis testing: the mechanics
1. Articulate a hypothesis
2. Identify its implications
3. Attempt to prove the implications
stemming from theory false.
4. Evaluate by looking at data
Data
Empirical evidence-information
about the state of the world.
The same research principles
always apply whether our data
are qualitative or quantitative
Types of Evidence
Qualitative evidence: The collection and
organization of evidence (data) using
particular facts (or often cases).
Quantitative evidence: The collection and
organization of evidence (data) using
numbers usually through statistics.
What Makes the Process
Scientific?
1.
2.
3.
4.
What Makes the Process
Scientific?
1. The goal is inference
What Makes the Process
Scientific?
The goal is inference:
Scientific research is designed to make
descriptive or explanatory generalizations
on the basis of empirical information.
What Makes the Process
Scientific?
The goal is inference (2 types)
Descriptive
A generalization about the state of the world based
on the small part that we see.
Causal
A generalization about how the world works based
on the small part that we see.
What Makes the Process
Scientific?
1. The goal is inference
2. The procedures are public
What Makes the Process
Scientific?
The procedures are public
Scientific research uses explicit, codified
and public methods to generate and
analyze data whose reliability can
therefore be assessed.
What Makes the Process
Scientific?
The procedures are public
Scientific research uses explicit, codified
and public methods to generate and
analyze data whose reliability can
therefore be assessed.
Results should be replicable.
What Makes the Process
Scientific?
1. The goal is inference
2. The procedures are public
3. The conclusions are uncertain
What Makes the Process
Scientific?
The conclusions are uncertain
Inference is an imperfect process. Without
an estimate of uncertainty a description
of the world is not very meaningful.
What Makes the Process
Scientific?
Two types of uncertainty:
Fundamental uncertainty: Uncertainty
inherent in the relationship between two
things.
Estimation uncertainty: Uncertainty in our
inference due to the methods we use to
draw the inference.
What Makes the Process
Scientific?
Fundamental uncertainty:
Uncertainty inherent in
the relationship between two things.
Example: Probability of getting lung cancer
Smoker
.34
Non-smoker .03
Not everyone who smokes gets lung cancer.
What Makes the Process
Scientific?
Two types of uncertainty:
Fundamental uncertainty: Uncertainty
inherent in the relationship between two
things.
Estimation uncertainty: Uncertainty in our
inference due to the methods we use to
draw the inference.
What Makes the Process
Scientific?
Estimation uncertainty:
Uncertainty in our inference due to
the methods we use to draw the
inference.
Example: public opinion poll
The uncertainty in our
estimates is a function
of how large the sample
is that we draw.
Sample
size (N)
Margin of
Error
100
10%
400
5%
900
3%
What Makes the Process
Scientific?
1.
2.
3.
4.
The goal is inference
The procedures are public
The conclusions are uncertain
The content of science is its (the) method
What Makes the Process
Scientific?
The content of science is its (the) method:
Scientific research adheres to rules on
which its validity depends.
These rules can be applied to the study of
any subject.
What Makes the Process
Scientific?
The content of science is its (the) method:
Scientific research adheres to rules on which its
validity depends.
These rules can be applied to the study of any
subject.
The possible subjects to be studied are endless
but the principles (rules) for studying them are
not.