Thought Leadership

Empirical researchers are increasingly faced with rich data sets containing many controls or instrumental variables, making it essential to choose an appropriate approach to variable selection. In this paper, we provide results for valid inference after post- or orthogonal L2-boosting is used for variable selection. We consider treatment effects after selecting among many control variables and instrumental variable models with potentially many instruments. To achieve this, we establish new results for the rate of convergence of iterated post-L2-boosting and orthogonal L2-boosting in a high-dimensional setting similar to Lasso, i.e., under approximate sparsity without assuming the beta-min condition. These results are extended to the 2SLS framework and valid inference is provided for treatment effect analysis. We give extensive simulation results for the proposed methods and compare them with Lasso. In an empirical application, we construct efficient IVs with our proposed methods to estimate the effect of pre-merger overlap of bank branch networks in the US on the post-merger stock returns of the acquirer bank.

Risk premia increase with government debt. Debt-to-GDP ratios positively predict stock returns at short and long horizons in the U.S. and other advanced economies. Higher debt is also associated with higher bond premia and lower risk-free rates. Major government debt theories (liquidity, safety, crowding out) either do not address or are inconsistent with these findings. New evidence suggests that the increased risk premia provide compensation for larger fiscal risk; during periods of elevated debt, fiscal policy becomes more uncertain and less effective and can lead to debt crises. I quantify these mechanisms in an equilibrium model.

Shared coupons, a new form of coupon, differ from coupons distributed directly from businesses (i.e., direct coupons) in that shared coupons combine two influential components: economic savings (e.g., $5 off) and social sharing (e.g., from friends). Using two lab experiments and two large-scale field experiments on social media, the authors find that regular shared coupons underperform direct coupons in terms of coupon redemption because of the norm conflict between economic incentives and communal relationships (i.e., friendships), whereas shared coupons with experience cocreation, in which coupon givers and coupon receivers must invest joint efforts to create a shared experience before redeeming the coupons, outperform direct coupons. Experience cocreation can advance social goals (e.g., building friendships), reduce the norm conflict, and thereby make customers more likely to share and to redeem coupons. The authors further investigate the effects of two strategies for driving the redemption of shared coupons with experience cocreation: changing the coupon's face value (low vs. high) and using ex post communication (social messages vs. economic messages). They find that social messages can make low-value coupons as effective as high-value coupons, thereby enabling the firm to “do more with less.”