# What is Endogeneity?

Statistical Analysis

In statistics, endogeneity refers to the correlation between the independent variable and unexplained variation (or “error”) in the dependent variable. In a regression analysis, for instance, endogeneity occurs when there is a relationship between the predictor variable and the error term. Endogeneity may lead to bias in the results of statistical tests. This is a crucial issue in statistics because endogeneity may undermine the validity of inferences and lead to incorrect conclusions.

##### Sources of Endogeneity

Endogeneity can arise in several ways. Omitted variable bias is one common source that occurs when researchers leave out a relevant predictor variable from the model. In such cases, the omitted variable may correlate with the included predictors and also influence the dependent variable, resulting in biased estimates. Endogeneity can also be caused by measurement error, sample selection bias, or simultaneity. Measurement error occurs when the values of the predictor variable are not measured accurately, leading to biased estimates. Sample selection bias occurs when the sample is not randomly selected, leading to a biased sample. Simultaneity occurs when the predictor and dependent variables causally influence each other. For example, education level and income may have a circular or bidirectional relationship. Having a lower level of education may limit a person’s potential earnings. But having low income could also prevent a person from obtaining a higher degree.

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Some techniques can address endogeneity in statistical analysis. One common approach is to use instrumental variables. These variables correlate with the predictor variable but do not directly relate to the dependent variable. Analysis of instrumental variables allows researchers to isolate the exogenous variation in the predictor variable and obtain a less biased estimate of its effect on the dependent variable. A technique that can help mitigate endogeneity in biased samples is the Heckman correction.

##### Conclusion

In conclusion, endogeneity is a critical issue in statistical analysis that can lead to biased results or inaccurate conclusions. It is important for researchers to be aware of the sources of endogeneity and to use appropriate techniques to address it. By doing so, they can ensure that their statistical analyses are valid and provide accurate insights into the phenomena under study.

Written By David Kovac

April 18, 2023