Qualitative vs. Quantitative
Research - 1
Qualitative and quantitative studies are
both types of observational studies.
Quantitative research measures differences
in number for variables, and usually studies
a large number of cases (Large “N”).
Qualitative research measures differences
in kind for variables, and usually studies a
small number of cases (Small “N”).
Qualitative vs. Quantitative
Research - 2
Because it covers a broad range of cases,
quantitative research yields conclusions
that can be generalized more widely (it
has the strongest external validity).
Because it looks closely at a few cases and
traces causal pathways, qualitative
research outperforms quantitative
research in its measurement validity and
internal validity (Do the independent
variables effect the dependent variable?)
Qualitative vs. Quantitative
Research - 3
When selecting cases for your quantitative
research sample, it is imperative that you
use random selection.
In qualitative research, “selection must be
done in an intentional fashion, consistent
with research objectives and strategy.”
Selecting Cases on the Independent
Variable - 1
“Selecting on the independent variable”
means “selecting your cases according
to the values of the independent variable
that they take on.”
In order to do this, you have to know a little
bit about all of your potential cases.
In order to do this right, you CANNOT act as
if you also know the values that the
dependent variable takes on.
Selecting Cases on the Independent
Variable - 2
The Most Similar Systems method selects
cases that take on similar values of
confounding variables, but different
values of a key independent variable.
This “holds constant” the confounds
because they take on the SAME values in
all of the cases.
Selecting Cases on the Independent
Variable - 3
The cases that you might select in a Most
Similar Systems design will differ based
on the research question you ask.
For example, Bill Clinton, Jimmy Carter and
Barack Obama for the impact of region on
voting (since all are Democrats you’ve
“controlled” for political party – not all three
are from the same region so region “varies”
– however, since region and race vary
together, race could be a “confound”).
Selecting Cases on the Independent
Variable - 4
The Most Different Systems method
selects cases that take on very different
values for multiple independent variables.
If it turns out that these cases all take on the
same value of a dependent variable, then
we can rule out the independent variables as
causes of the dependent variable. Such a
situation would mean that we could only
disprove a hypothesis. That’s why we
typically avoid this method.
Income Inequality and Civil War
Income
Inequality
Poverty
Colonial Past
External Threat
Civil
War
Income Inequality and Civil War
Case
Costa
Rica
Income
Poverty Colonial External
Inequality
Past
Threat
Moderate Yes
Yup
Nope
El
High
Salvador
Yes
Yup
Nope
Cuba
Yes
Yup
Nope
High
Income Inequality and Civil War
Case
Civil War?
Costa Rica No
El
Salvador
Yes
Cuba
Yes
We can hold the
confounds constant
by selecting these
similar cases from
Latin America.
It appears that
income inequality
does lead to civil
war.
Selecting on the Dependent
Variable - 1
Selecting cases according to the value of
the dependent variable that they take on
is more controversial than selecting on
the independent variable.
It is crucial to select observations WITHOUT
regard to values of the independent
variables.
Selecting on the Dependent
Variable – 2
When you use Mills’ Method of Agreement,
you select cases that take on the SAME
values of the dependent variable.
This helps you to rule out possible causes,
because independent variables that vary over
these cases CAN’T cause the dependent var.
This method can only DISPROVE a
hypothesis, because it can’t find a correlation.
Selecting on the Dependent
Variable - 3
This design could help us rule out “early
industrialization” as a cause of whether
a country has a viable socialist party.
Case
France
Early
Industrialization?
No
Viable Socialist
Party?
Yes
Britain
Yes
Yes
Selecting on the Dependent
Variable - 4
When you use Mills’ Method of Difference,
you select cases that take on
DIFFERENT values of the dependent
variable.
After you have selected your cases, you
determine what values they take on for
some independent variables.
Perhaps one independent variable will vary
across your cases, and explain the D.V.
Selecting on the Dependent
Variable - 5
Adding a country that has no viable
socialist party can add causal leverage
to our early investigation.
Case
Early Indust.? Feudalism? Viable Social
Party?
France
No
Yes
Yes
Britain
Yes
Yes
Yes
USA
Yes
No
No
Comparing Many Research
Methods: Measurement Validity
Measurement validity judges the gap
between your conceptual definition and
your operational definition.
Qualitative – Highest measurement validity
The measurement validity of other research
methods (Lab experiments, quasi/natural
experiments, and quantitative research)
really depends on what you are trying to
measure.
Comparing Many Research
Methods: Internal Validity
Internal validity judges how well a research
design has tested a causal relationship,
in the cases examined. Random
assignment is the key.
Lab Experiments – highest
Quasi/Natural experiments – medium
Qualitative research – medium
Quantitative research – lowest
Comparing Many Research
Methods: External Validity
External validity is how confident we can
be that a causal relationship identified in
our cases can be generalized to the
outside world. Random sampling is key
Quantitative research – highest
Quasi/Natural experiments – medium
Lab experiments – low
Qualitative research – low
Comparing Many Research
Methods: Overall Lessons
The best research design depends on
your research question and the
particular problems that it poses.
The best research uses a mixture of
methods to test a hypothesis.