Date:         Fri, 23 Sep 2005 11:43:48 +0100
Reply-To:     Alice Sullivan <A.Sullivan@ioe.ac.uk>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Alice Sullivan <A.Sullivan@ioe.ac.uk>
Subject:      Propensity score matching
Content-Type: text/plain; charset="us-ascii"

Hi,

 

I am doing an analysis of academic outcomes for children in private and
state schools, and am trying to use the propensity score approach.

 

I want to match on the exact propensity score, dropping unmatched cases
from the sample. I did try the binning approach, but since my dataset is
large (more than 10,000 cases), it was impossible to balance the bins.

 

I have calculated the propensity score using 'save predicted values -
probabilities' in binary logistic regression, with the 'treatment'
(state/private school) as the dependent variable, and a set of
predictors (social class, etc), as follows:

 

LOGISTIC REGRESSION  private

  /METHOD = ENTER region3s faclas7m educatio famtrad kidno mobooks moint
Zabilit11 teacha_1 teachmiss abilmiss

  /CONTRAST (region3s)=Indicator  /CONTRAST (faclas7m)=Indicator
/CONTRAST (educatio)=Indicator  /CONTRAST

  (famtrad)=Indicator  /CONTRAST (kidno)=Indicator  /CONTRAST
(mobooks)=Indicator  /CONTRAST (moint)=Indicator  /CONTRAST

  (abilmiss)=Indicator  /CONTRAST (teachmiss)=Indicator

  /SAVE = PRED

  /CRITERIA = PIN(.05) POUT(.10) ITERATE(20) CUT(.5) .

 

My problem is that the number of values I get from this is huge -  it
exceeds 1000, so I can't even run a crosstabs. I can run a table of
frequencies, but it's too huge to print out.

 

My questions are:

1.      Am I doing something wrong?
2.      Is it acceptable to group the propensity scores together - e.g.
into percentiles or deciles, before dropping unmatched cases, or would
this defeat the object? 
3.      Has anyone written syntax to identify/drop unmatched cases?
(Doing it by hand is a daunting task with so many values!).

 

Many Thanks,

Alice

 

 

Dr. Alice Sullivan

Centre for Longitudinal Studies

Institute of Education

20 Bedford Way

LONDON

WC1H OAL