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  • System-gmm xtabond2 - Correct specifications of additional lags of a regressor in the instrument set?

    Dear statalist users,

    I am using xtabond2 in Stata 13.1 to estimate the effects of police inspections on the crime rate, considered as endogenous. The other regressors are considered predetermined. However, I have a doubt about how to properly specify L(0/1).inspections in the instrument set.

    Here is the code:

    xtabond2 crime L.crime L(0/1).(inspections) assoc_rate Education lgdp unem den y2009-y2016, ///
    gmmstyle(crime inspections, collapse laglimits(2 4) eq(diff)) ///
    gmmstyle(assoc_rate Education lgdp unem den, collapse lag(1 3) eq(diff)) ///
    ivstyle(LD.(crime inspections), eq(level) mz) ///
    ivstyle(D.assoc_rate D.Education D.lgdp D.unem D.den, eq(level) mz) ///
    ivstyle(y2009-y2016, eq(level) mz) ///
    robust small artests(3)

    Is it the correct specification for the endogenous regressors or should I specify it as:
    gmmstyle(crime inspections L.inspections, collapse laglimits(2 4) eq(diff)) ///
    ivstyle(LD.(crime inspections L.inspections), eq(level) mz) ///
    ?

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