st: Instrumental variable design: no control group

[John Antonakis <John.Antonakis@unil.ch>]

I have estimated the following model in STATA:

(where participant i is measured on two occassions)

xi: xtivreg y (mv = prepost) controls i.rater i.participant, re robust

Where:

prepost = a dummy variable (0=pretreatement, 1=posttreatment)

mv =  the manipulated check (i.e., a manipulation check to see whether 
the participants actually responded to the treatment)

controls = refers to participant individual difference controls (e.g., 
personality variables, age, set)

i.rater = rater fixed effects (given that groups of raters rated the 
participant on the DV)

i.participant = participant fixed effects (given that participants were 
rated twice)

Now this design does not have a control group. It would have been 
stronger if it did, but I could not randomly assign individuals to a 
treatment and control. Everyone had to receive the treatment. The way to 
mitigate this limitation was to measure the manipulation and then 
regress the DV on the manipulation (instrumented by the prepost dummy). 
My thinking is that the manipulation check serves as the independent 
endogenous variable and the intervention dummy variable as the exogenous 
treatment. If the change in y is predicted by the manipulation check, 
which in turn is predicted by the prepost treatment, then I can be more 
certain about our causal deductions as compared a simple repeated 
measures design in which the manipulation check does not serve as the 
endogenous independent variable. Because the manipulation check is 
modelled as a predictor, other putative causes can, for most intents and 
purposes, be ruled out.

Has anyone seen a published example of such as design that they can 
point me to? If so, is there a particular name given to this design or 
is it simply a IV design? Also, any suggestions on how to improve causal 
deduction?

Thanks,
J.

--
____________________________________________________

Prof. John Antonakis
Associate Dean 
Faculty of Business and Economics
University of Lausanne
Internef #618
CH-1015 Lausanne-Dorigny
Switzerland

Tel ++41 (0)21 692-3438
Fax ++41 (0)21 692-3305

http://www.hec.unil.ch/people/jantonakis&cl=en
____________________________________________________

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