No class this Thursday.

Transcription

1 No class this Thursday.

2 Homework #4 is due Friday by 5pm. Homework #5 is due Friday, March 14 th, by 5pm.

3 Political Science 15 Lecture 16: Small-N Methods

4 Qualitative vs. Quantitative Research Large-N studies look for patterns in a large number of cases. Random selection of cases. Small-N studies examine a small number of cases in depth. Deliberate selection of cases. Usually large-n approaches have better external validity, while small-n approaches have better internal validity and measurement validity. Probabilistic versus deterministic causation.

5 Types of Small-N Methods The comparative method. Based on J.S. Mill s System of Logic (1843). Most-similar method ( method of difference ). Most-different method ( method of agreement ). Qualitative comparative analysis (QCA). Case study methods (when N = 1).

6 The Comparative Method: Most-Similar Design The most-similar method is the most common approach to small-n research problems in political science. Examine a handful of cases that are as similar as possible, except on the outcome of interest (the dependent variable). Similarity of cases means we control for many alternative explanations. If one factor is different between cases, and outcome is different, this is our probable cause for the outcome.

7 Example: Causes of Revolution Potential Causes England France Repressive Monarchy Nonpropertied Agrarian Proletariat Expensive Foreign Wars Stagnant Standard of Living No Outcome Stability Revolution

8 Example: Dreze and Sen Potential Causes India China Disadvantaged Beginning Moderate Economic Growth Adequate Calories Per Person System to Distribute Public Resources No Life Expectancy 57 69

9 Problems with the Most-Similar Method We generally treat the independent variables as something simple (yes/no, for instance). The more complicated the operationalization, the harder this method is to do. Deterministic causality. Multiple causal factors and causal complexity are hard or impossible to determine. External validity is low.

10 The Comparative Method: Most-Different Design This is the opposite of the most-similar method. Examine a handful of cases that are as different as possible, except on the outcome of interest (the dependent variable), which is the same. Difference of cases means we control for many alternative explanations. If one factor is the same between cases, and outcome is the same, this is our probable cause for the outcome.

11 Example: Causes of Revolution Potential Causes China (1927) France (1789) Repressive Monarchy No Nonpropertied Agrarian Proletariat Expensive Foreign Wars No Stagnant Standard of Living No Outcome Revolution Revolution

12 Problems with the Most-Different Method As with the most-similar method, we can t use complicated variable codings, multiple causal factors are hard or impossible to determine, and external validity is low. Deterministic causality. Case selection on the dependent variable without variation on the dependent variable determining causality is extremely difficult. This method is more useful for ruling out necessary causes than determining causality.

13 Qualitative Comparative Analysis (QCA) A medium-n method (N between a few and 50 or so). A middle ground. Independent variables are coded as binary (yes/no). Sequences of these variables are entered into a truth table. Reach conclusion through Boolean logic which combinations of factors produce which outcomes?

14 Example: Military Coups Cases Internal Military Conflict Death of Dictator CIA Involvement Coup?

15 Problems with QCA As with small-n methods, we can t use complicated variable codings. Deterministic causality. However, multiple causal factors/causal complexity can possibly be distinguished, and external validity is higher. A tradeoff between large-n and small-n positive traits.

16 Case Studies These are methods of examining a single case. In a sense we have an N of 1, but we must make some kind of comparison in order to make a causal inference, either within or across cases. This comparison can be implied. Internal and measurement validity very high, external validity very low we know a lot about one case, but very little about how our observations will generalize.

17 Case Study Methods Extreme Case: A clear example of a hard-to-measure concept: Nazi Germany for Fascism, North Korea for isolated state. Typical Case: Examine a representative or average case in depth. Crucial Case: Classic examples of a concept, or most/least likely cases. Counterfactual Case: Consider causality if an independent variable had a different value. Can combine case studies to examine a range of cases (e.g., two extreme cases, one from each end of the spectrum).

18 Small- versus Large-N Methods All methods are a tradeoff between internal, external, and measurement validity. Small-N lets us go more in depth into our cases, but generalizing is harder. No matter the method, our goal is the same. We want to make a causal inference and learn how the world works.