Re: st: how to handle missing observations in a regression model

[Richard Williams <Richard.A.Williams.5@ND.edu>]

At 03:32 AM 9/5/2006, Simo Hansen wrote:
> Dear All;
> I am using moter's years of schooling and father's years of schooling as
> explanatory variables in my regression model. I also creata a dummy
> indicators for whether mother's and father's years of schooling are missing,
> respectively:
> gen misdaded=dadedec==.
> gen mismoted=moteduc==.
> When I run the following regression:
> reg childedyrs dadeduc moteduc misdaded mismoted,
> Stata drops two dummy indicators for whether parents' schooling is missing.
> Do you have any suggestion on how I can properly control for whether
> mother's and father's years of schooling are missing in my regression model.
Did you also do something like assign the mean to the missing cases 
on dadeduc and moteduc?  If not, all the missing cases are still 
getting dropped, and dadeduc and moteduc then get dropped because 
they always equal 0 (non-missing) for the cases being analyzed.

The technique that I think you are using is discussed (along with 
Stata commands) on pp. 5-6 & 10-12 of the following handout:

http://www.nd.edu/~rwilliam/stats2/l12.pdf

HOWEVER, note that the approach, while once popular, has come to be 
discredited; as Allison points out in his Sage book "Missing Data", 
"the method generally produces biased estimates of the coefficients."


-------------------------------------------
Richard Williams, Notre Dame Dept of Sociology
OFFICE: (574)631-6668, (574)631-6463
FAX:    (574)288-4373
HOME:   (574)289-5227
EMAIL:  Richard.A.Williams.5@ND.Edu
WWW (personal):    http://www.nd.edu/~rwilliam
WWW (department):    http://www.nd.edu/~soc 
*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/