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Other examples of
multiple regression in research: Predicting African
coups
Wells: "The Coup d'Etat in Theory and Practice:
Independent Black Africa in the 1960s"
- Wells notes that most
scholars said that it was impossible to specify
variables which would distinguish countries that had
coups in the 1960s from those that did
not.
- He built a
dependent variable -- "coup activity score" -- by
assigning 10 points for a successful coup, 3 for an
overt attempt that failed, and 1 point for an
uncovered plot.
- He identified 15
likely causal variables of coup activity, conceptually
grouped into
- 8 socioecnomic
factors
- 7 military
factors
- The simple
correlations predicting to coup activity for 31
nations averaged about .10 for the socioeconomic
variables and .30 for the military
variables
- Used multiple
regression to combine these factors
- The 8
socioeconomic variables yielded an R of .41,
R2 = .16
- The 7 military
variables gave an R of .48, R2 =
.23
- Together, they
gave an R of .75, R2 = .56
- Conclusion was
that a model can be constructed that explains a
substantial proportion of coup activity
- Problems with
the analysis -- done over a decade ago
- Erroneous
claim: "The [beta] coefficients are
interpreted as unstandardized partial correlations
and indicate the contribution of each variable to
the total explained variance in the dependent
variable." (pp.883-884) What is wrong about this
statement?
- Table 4, which
reports the "[beta] coefficients and
multiple correlations" provides insufficient
information to judge the analysis -- e.g., no idea
of level of significance set for the
coefficients
- The combined
analysis, which explained 56% of the variance, used
15 variables for 31 cases -- what is the problem
here?
Jackman: "The Predictability of Coups d'Etat: A
model with African Data"
- Jackman's article is
more sophisticated than Wells, and you are not
expected to understand it all.
- Jackman explained 79%
of the variance in coups for 29 countries with only 7
variables
- The variables were
entirely different from Wells'
- Social
mobilization
- Pluralism (size of
ethnic group)
- Party
strength
- Turnout
- In general, Jackman's
work was more theoretically oriented and better
executed than Wells'.
These readings were chosen to illustrate the point that
to understand and analyze the current literature in
political science, one needs to know something about the
methodology employed.
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