Abstract This article develops the uniform asymptotic theory for local projection (LP) regression when the true lag order of the model is unknown and potentially infinite. The theory allows for varying degrees of persistence in the data, growing response horizons, and general conditionally heteroskedastic martingale-difference shocks. Based on the theory, we make two main contributions. First, we show that LPs can achieve semiparametric efficiency at a given horizon under classical assumptions on the data, provided that the controlled lag order diverges. Thus, the commonly perceived efficiency loss of LPs can become asymptotically negligible with many controls. Second, we propose LP-based inference procedures for (level and cumulated) impulse responses that possess robustness properties not shared by existing methods. Inference methods using two distinct standard errors are considered. The uniform validity for the first method depends on a zero fourth-order cumulant condition on shocks, while that of the second holds more generally for conditionally heteroskedastic martingale-difference shocks. We propose a bootstrap procedure that improves finite-sample performance and extend the standard error construction to structural responses.

Government regulations on housing flippers target their high capital gains but ignore their risk-sharing function: rational arbitrageurs reduce market return volatility borne by other participants while undertaking high idiosyncratic risk. Regulations that tighten the limits of arbitrage in housing markets can adversely affect market efficiency by blocking this risk-sharing function. Using comprehensive housing transaction records in Hong Kong from 1993 to 2021, we find although flippers obtain higher annual capital gain returns than long-term buyers by 8.76 percentage points, they undertake substantially higher idiosyncratic risk due to its unique downward-sloping term structure. Only experienced flippers, who have at least two prior purchase experiences and constitute less than 20% of the flippers, outperform long-term buyers in risk-adjusted returns. Following the enactment of an anti-speculation policy that decreases the share of flippers by 14.2 percentage points in one year, the market return volatility of the entire housing market increases by 21.9%.