Before revision:  For this, an appropriate Lasso-technique is crucial in order to identify the magnitude and significance of the effect due to potentially many relevant controlling factors and only a short time frame where fees existed. We show that a post-double selection strategy combined with stability selection determines a significant negative impact of  fees on student enrollment and identifies relevant variables .
After revision:  For this, an appropriate Lasso-technique is crucial in order to identify the federal average causal effect of tuition fees by controlling for a large amount of potentially influencing attributes for state heterogeneity. We suggest a stability post-double selection strategy combined with stability selection determines a significant negative impact of fees on student enrollment and identifies relevant variables .