handout - Daina Chiba

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2.2 Additional Tips 2.2.1 Rescaling If one of your coefficients exceeds 10 in absolute values, consider rescaling the variable. If it exceeds 1, 000, you simply must rescale it. Coefficients greater than 1, 000, 000 are not only ugly but also misleading. There are several ways to rescale a variable, none of which changes the statistical results substantively. • Multiply the variable with some number (a natural choice would be 10 x with x = {−3, −2, −1, 1, 2, 3}, for example). • Standardize the variable (subtract its mean and then divide it with its standard deviation). After standardization, the variable has 0 mean and a unit variance. You can apply either one of the above to some or all of the variables included in your regression. Table 2: Models with rescaled Trade variables (1) (2) (3) (4) original multiply standardizeOne standardizeALL Lower trade-to-GDP ratio -32.262 ∗∗∗ -0.323 ∗∗∗ -0.094 ∗∗∗ -0.094 ∗∗∗ (-3.59) (-3.59) (-3.59) (-3.59) Lower democracy -0.069 ∗∗∗ -0.069 ∗∗∗ -0.069 ∗∗∗ -0.403 ∗∗∗ (-8.55) (-8.55) (-8.55) (-8.55) Higher democracy 0.038 ∗∗∗ 0.038 ∗∗∗ 0.038 ∗∗∗ 0.256 ∗∗∗ (5.69) (5.69) (5.69) (5.69) Allies 0.075 0.075 0.075 0.018 (0.75) (0.75) (0.75) (0.75) Observations 464953 464953 464953 464953 Log lik. -8118.156 -8118.156 -8118.156 -8118.156 Chi-squared 3861.950 3861.950 3861.950 3861.950 t statistics in parentheses ∗ p < 0.05, ∗∗ p < 0.01, ∗∗∗ p < 0.001 We can see in the above table that results are identical after (2) multiplication of one variable (3) standardization of one variable or (4) standardization of all variables. 8
2.2.2 Putting Stars For the sake of convenience, I think it is good to highlight statistically significant coefficients in some ways. I have no objection to putting stars, but keep in mind that there are some people who think putting stars is a sin. Some of those people who hate stars, however, think that it is OK to highlight statistically significant coefficients by writing them in thick font (I honestly don’t know why). If, unfortunately, your reviewer or your TA expresses such a belief, you’d better listen to him than trying to point out the stupidity of that person. FYI, AJPS prohibits us from placing multiple stars to differentiate multiple confidence levels. 2.3 Exporting Stata Results to R This will become essential when you need to estimate some fancy statistical models that are easier to implement in Stata, but then want to use R to make graphs. Run the following chunk of Stata code: Stata code insheet using "output/smw06162010dataS.txt", clear global covariates "smldem lrgdem smldep allies lncaprat dircont lndstab majpower" replace smldep = smldep*1000 logit mzmid1 $covariates mat beta = e(b) mat vcov = e(V) // Export Beta and V-COV matrix preserve svmat beta, names(matcol) outsheet beta* in 1 using "output/sr_beta.txt", replace nolabel restore preserve svmat vcov, names(matcol) outsheet vcov* in 1/9 using "output/sr_vcov.txt", replace nolabel restore Two text files will be created (replaced) within the output folder. 9
Page 1 and 2: Contents Summer Methods Workshop: P
Page 3 and 4: Stata code use "output/smw06162010d
Page 5 and 6: 2.1.3 Exporting Stata Results to a
Page 7: 2.1.4 Exporting Stata Results to Wo
Page 11 and 12: Now, as you select several lines of
Page 13 and 14: 3.2 Calculating Substantive Effects
Page 15 and 16: Now, we have set X by“column bind
Page 17 and 18: 3.4 Plotting Substantive Effects: W
Page 19: 3.6 Plotting Regression Coefficient

handout - Daina Chiba

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