[amelia] ameliabind and zelig

Hi, I want to combine multiple amelia runs, and use the zelig function on the entire set of amelia outputs. However, I noticed that when I run zelig on the combined set, the coefficients don't look right. Here are the script and the R outputs: ## Amelia II: Multiple Imputation ## (Version 1.7, built: 2013-02-10) Attaching package: ‘zoo’ The following object(s) are masked from ‘package:base’: as.Date, as.Date.numeric ZELIG (Versions 4.1-3, built: 2013-01-30) -- Imputation 1 -- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 -- Imputation 1 -- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Amelia output with 2 imputed datasets. Return code: 1 Message: Normal EM convergence Chain Lengths: -------------- Imputation 1: 14 Imputation 2: 15 Rows after Listwise Deletion: 96 Rows after Imputation: 171 Patterns of missingness in the data: 8 Fraction Missing for original variables: ----------------------------------------- Fraction Missing year 0.00000000 country 0.00000000 tariff 0.33918129 polity 0.01169591 pop 0.00000000 gdp.pc 0.00000000 intresmi 0.07602339 signed 0.01754386 fiveop 0.10526316 usheg 0.00000000 # run zelig on the first amelia run Call: lm(formula = formula, weights = weights, model = F, data = data) Residuals: Min 1Q Median 3Q Max -29.686 -11.067 -3.367 10.003 45.556 Coefficients: Estimate Std. Error t value Pr(>|t|) (Intercept) 3.317e+01 1.891e+00 17.538 < 2e-16 *** polity -1.060e-01 2.434e-01 -0.435 0.664 pop 2.925e-08 5.405e-09 5.411 2.15e-07 *** gdp.pc -2.738e-03 5.235e-04 -5.231 4.99e-07 *** --- Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 Residual standard error: 16.62 on 167 degrees of freedom Multiple R-squared: 0.3234, Adjusted R-squared: 0.3112 F-statistic: 26.6 on 3 and 167 DF, p-value: 4.07e-14 # run zelig on the second amelia run Call: lm(formula = formula, weights = weights, model = F, data = data) Residuals: Min 1Q Median 3Q Max -40.13 -11.72 -3.63 10.16 43.77 Coefficients: Estimate Std. Error t value Pr(>|t|) (Intercept) 3.400e+01 1.984e+00 17.133 < 2e-16 *** polity -6.123e-02 2.545e-01 -0.241 0.81 pop 3.289e-08 5.689e-09 5.781 3.56e-08 *** gdp.pc -3.016e-03 5.501e-04 -5.484 1.51e-07 *** --- Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 Residual standard error: 17.47 on 167 degrees of freedom Multiple R-squared: 0.3495, Adjusted R-squared: 0.3378 F-statistic: 29.91 on 3 and 167 DF, p-value: 1.574e-15 # run zelig on the combined amelia runs Call: lm(formula = formula, weights = weights, model = F, data = data) Residuals: Min 1Q Median 3Q Max -29.686 -11.067 -3.367 10.003 45.556 Coefficients: Estimate Std. Error t value Pr(>|t|) (Intercept) 3.317e+01 1.891e+00 17.538 < 2e-16 *** polity -1.060e-01 2.434e-01 -0.435 0.664 pop 2.925e-08 5.405e-09 5.411 2.15e-07 *** gdp.pc -2.738e-03 5.235e-04 -5.231 4.99e-07 *** --- Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 Residual standard error: 16.62 on 167 degrees of freedom Multiple R-squared: 0.3234, Adjusted R-squared: 0.3112 F-statistic: 26.6 on 3 and 167 DF, p-value: 4.07e-14 Can someone please tell me why summary(z.out3) is returning the exact same results as summary(z.out1)? How can I fix this problem so that the ameliabind output is treated the same as a direct output from the amelia function? Thanks.