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From |
nicola.baldini2@unibo.it |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Mediating variables |

Date |
Wed, 08 Oct 2008 19:01:43 +0200 |

I am not sure if and how it fits the discussion, but may -sgmediation- (found on http://www.ats.ucla.edu/stat/stata/ado/analysis) help? it performs Sobel-Goodman mediation tests Nicola P.S. I'll NOT receive/read any email but the Digest. At 02.33 06/10/2008 -0400, you wrote: >Dear Stata users >I have a model in which the relationship between a predictor ?x? and an >outcome ?y? is mediated by three factors (?r?, ?s? and ?t?). I am only able >to test whether one of the predictors (?r?) mediates the relationship >between ?x? and ?y? (I only have data on this mediating variable and I >cannot get data on the other two). I would like to implement Baron and Kenny >(1986)?s test for mediation. At least, this involves estimating the >following system: >Y=a1+b*r+c*x+epsilon1 >r=a2+d*x+epsilon2 >Given that the errors of the two equations are potentially correlated, it >has been suggested that a 2SLS approach should be used. I have seen that >this could be done with ivregress, provided that I can find data on at least >one variable that affects ?r? and does not affect ?y?. My doubts are the >following: >1) Given that I have a triangular system, do I have to use the >traditional approach implemented by ivregress or the ?modified? proposed in >http://www.stata.com/support/faqs/stat/ivr_faq.html ? Are both valid? >2) How do I test for the hypothesis that the errors are correlated? I >have seen that the use of a Hausman test is suggested in the literature, but >I do not know how to implement this in Stata (specially in the case I use >the ?modified? approach) >3) Given that I have panel data, could I take advantage of the panel >structure of my data to correct for the fact that I do not have information >on two of the mediating variables (?s? and ?t?)? Is there a procedure in >Stata for that? >Thanks a lot >Jaime Gómez >Universidad de Zaragoza * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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