*Post-Double-Lasso is becoming the most popular method for estimating linear regression models with many covariates when the purpose is to obtain an accurate estimate of a parameter of interest, such as an average treatment effect. However, this method can suffer from substantial omitted variable bias in finite sample. We propose a new method called Post-Double-Autometrics, which is based on Autometrics, and show that this method outperforms Post-Double-Lasso. Its use in a standard application of economic growth sheds new light on the hypothesis of convergence from poor to rich economies.

**I analyse the transmission of Quantitative Easing and assess its distributional effects in a heterogeneous monetary union. Focusing on European Monetary Union (EMU), I capture two types of heterogeneity: cross-country –- debt profiles (long-term debt liquidity, short-term to long-term debt, debt-to-GDP ratio) and within-country heterogeneity -- unequal households financial participation. I develop a Two-Country, Two-Agent New Keynesian model with a liquidity constraint, calibrated to EMU core and peripheral countries during the Global Financial Crisis. My main finding is that heterogeneity within a monetary union critically shapes the impact of Quantitative Easing. Across countries, differences in debt profiles shape the the aggregate response of output via the portfolio rebalancing channel. Bond liquidity governs the strength of the portfolio reallocation while short-to-long-term debt ratio drives the direction of these reallocations. Within countries, disparities in households’ access to financial markets condition both the aggregate output response and the distributional effects of Quantitative Easing.