Problem Description:
The STATA assignment aims to investigate the potential correlation between the variable "choiceyrs" and the error term in a regression model. This correlation arises due to endogeneity, indicating a need for careful examination. The dataset comprises 990 students, with varying experiences related to school vouchers and private school attendance.
- Endogeneity of "choiceyrs": The correlation between "choiceyrs" and the error term is attributed to endogeneity. This suggests that "choiceyrs" is endogenous in the equation, and further analysis is required to address this issue.
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Descriptive Statistics: Out of 990 students:
- 468 students were never awarded vouchers.
- 522 students had vouchers available for four years.
- 470 students attended a choice school for four years.
- Regression Analysis:The regression of "choiceyrs" on "selectyrs" is conducted to explore the relationship. The coefficient on "selectyrs" is 0.7668, indicating that a unit increase in the number of years a student is selected for a voucher correlates with a 0.7668 increase in the number of years spent in a private school. The positive relationship is evident, but the endogeneity of "selectyrs" is tested, and results suggest non-rejection of the null hypothesis.
- Impact on Academic Performance: Regression of "mnce" (math score) on "choiceyrs" reveals a negative relationship. The coefficient of -1.8370 implies that an increase in the number of years a student attends a private school leads to a decrease in math scores.
- Instrumental Variable (IV) Analysis: A regression of "mnce" on "choiceyrs" is performed with "selectyrs" as the instrumental variable. However, the use of IV does not demonstrate a positive effect of attending a private school on math scores, as indicated by the coefficient on "choiceyrs."
- Improved Effect through Instrumenting: The coefficient on "choiceyrs" in the IV analysis provides a refined understanding of the effect of attending a private school on math scores. This instrumental variable approach enhances the precision of the estimation and contributes to a more accurate assessment of the impact of school choice on academic performance.
Table 1: The coefficients of choiceyrs
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