Dear experts,
in my previous post I explained my research proposal a little more in detail. Since I have evaluate certain firm resources upon firm performance, I find a "standard" OLS regression suitable in my case. In addition, I believe that one indep. variable in my list is endogenous. Therefore, I find etregress a suitable tool to account for endogeneity with a growth as well as a selection equation. The concern I am having now is, whether or not my data suffers from sample selection bias that I need to account for in my calculations (Heckman, Inverse Mills Ratio).
My sample represents answers from a survey that I sent to the total population of spin-off companies a research institute (the largest and most representative one in the country) has ever spun out. From these companies I contacted, none ceised to exist (bancruptcy, merger, etc.) up to the survey date. Thus, survivorship bias is not a problem of my primary concern, is it? Of course, not all firms answered my survey, the response rate amounts to almost 90% however. Of course, firms are not alike, having a response rate of 90% should nevertheless be sufficient reason to believe that my sample is (more or less) balanced and representative.
Of course there is many sample selection bias (undercoverage bias, voluntary response bais)...but those a standard limitations in a majority of sample-based studies I believe.
My ultimate question is, do you see a bias that Iam not aware of and which I need to correct for in case to avoid having biased estimates? As mentioned, I research firm resources on firm performance (measured by revenue growth, etc.) and one endogenous variable (external investment=treatment). My sample has of course a few missing data points in the dependent variable Y (firm growth) since not all firms wanted to provide the data. AND, I do have the data only in one state, namely the growth for firms having received the treatment and for those who have not. Not vice versa. Do you believe I need to correct for sample bias via a Inverse Mills Ratio or similar measure?
Any help is much appreciated!
Alex
in my previous post I explained my research proposal a little more in detail. Since I have evaluate certain firm resources upon firm performance, I find a "standard" OLS regression suitable in my case. In addition, I believe that one indep. variable in my list is endogenous. Therefore, I find etregress a suitable tool to account for endogeneity with a growth as well as a selection equation. The concern I am having now is, whether or not my data suffers from sample selection bias that I need to account for in my calculations (Heckman, Inverse Mills Ratio).
My sample represents answers from a survey that I sent to the total population of spin-off companies a research institute (the largest and most representative one in the country) has ever spun out. From these companies I contacted, none ceised to exist (bancruptcy, merger, etc.) up to the survey date. Thus, survivorship bias is not a problem of my primary concern, is it? Of course, not all firms answered my survey, the response rate amounts to almost 90% however. Of course, firms are not alike, having a response rate of 90% should nevertheless be sufficient reason to believe that my sample is (more or less) balanced and representative.
Of course there is many sample selection bias (undercoverage bias, voluntary response bais)...but those a standard limitations in a majority of sample-based studies I believe.
My ultimate question is, do you see a bias that Iam not aware of and which I need to correct for in case to avoid having biased estimates? As mentioned, I research firm resources on firm performance (measured by revenue growth, etc.) and one endogenous variable (external investment=treatment). My sample has of course a few missing data points in the dependent variable Y (firm growth) since not all firms wanted to provide the data. AND, I do have the data only in one state, namely the growth for firms having received the treatment and for those who have not. Not vice versa. Do you believe I need to correct for sample bias via a Inverse Mills Ratio or similar measure?
Any help is much appreciated!
Alex
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