A common misconception of missing data methods is the assumption that imputed values should represent "real" values. The purpose when addressing missing data is to correctly reproduce the variance/covariance matrix we would have observed had our data not had any missing information.
http://www.ats.ucla.edu/stat/stata/seminars/missing_data/Multiple_imputation/mi_in_stata_pt1_new.htm
Every time I think I know what's going on, suddenly there's another layer of complications.
2016年7月27日星期三
2016年7月5日星期二
2016年6月30日星期四
2016年6月8日星期三
2016年5月23日星期一
Proc MI FCS
http://sas-and-r.blogspot.com.au/2011/09/example-94-new-stuff-in-sas-93-mi-fcs.html
filename myhm url "http://www.math.smith.edu/sasr/datasets/helpmiss.csv" lrecl=704; proc import replace datafile=myhm out=help dbms=dlm; delimiter=','; getnames=yes; run; proc mi data = help nimpute=20 out=helpmi20fcs; class homeless female; var i1 homeless female sexrisk indtot mcs pcs; fcs logistic (female) logistic (homeless); run;
In the fcs statement, you list the method (logistic, discrim, reg, regpmm) to be used, naming the variable for which the method is to be used in parentheses following the method. (You can also specify a subset of covariates to be used in the method, using the usual SAS model-building syntax.) Omitted covariates are imputed using the default reg method.
ods output parameterestimates=helpmipefcs covb = helpmicovbfcs; proc logistic data=helpmi20fcs descending; by _imputation_; model homeless=female i1 sexrisk indtot /covb; run; proc mianalyze parms=helpmipefcs covb=helpmicovbfcs; modeleffects intercept female i1 sexrisk indtot; run;
with the following primary result:
Parameter Estimate Std Error 95% Conf. Limits intercept -2.492733 0.591241 -3.65157 -1.33390 female -0.245103 0.244029 -0.72339 0.23319 i1 0.023207 0.005610 0.01221 0.03420 sexrisk 0.058642 0.035803 -0.01153 0.12882 indtot 0.047971 0.015745 0.01711 0.07883
2016年5月22日星期日
Distribution Theory of the Non-Central Chi-Square
https://turing.une.edu.au/~stat354/notes/node47.html
2016年5月3日星期二
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