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From | "Dimitriy V. Masterov" <dvmaster@gmail.com> |
To | Statalist <statalist@hsphsun2.harvard.edu> |
Subject | Re: st: IV and matching estimator |
Date | Wed, 9 Jan 2013 09:35:15 -0800 |
Ayman, If I understand your problem, you have selection on unobservables. People who are enthusiastic consumers are likely to both see lots of advertisements as they are browsing and are also likely to buy or convert. Presumably, this creates a positive correlation between the error term and the impressions variable, so you get biased results with OLS. Unfortunately, propensity score matching will only deal with the selection on observables problem, so I don't think this sort of approach will work. DVM On Tue, Jan 8, 2013 at 7:23 PM, Ayman Farahat <ayman.farahat@yahoo.com> wrote: > am interested in evaluating the marginal effect of seeing an advertising impression on conversion (binary). > However, because of activity bias , the number of impression seen is correlated with the unobserved error and are therefore exogenous. > > I was thinking about using an IV to get around this problem. The instruments that I have are number of impressions of similar users on that day. > That seems very much like a matching estimator. > > Is this possible? Is there a way of doing this in Stata? > Best > Ayman > > > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/faqs/resources/statalist-faq/ > * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/