Creating I-Communities for the Modern Business

Zadanie pt. „Digitalizacja i udostępnienie w Cyfrowym Repozytorium Uniwersytetu Łódzkiego kolekcji czasopism naukowych wydawanych przez Uniwersytet Łódzki” nr 885/P-DUN/2014 zostało dofinansowane ze środków MNiSW w ramach działalności upowszechniającej nauk

Mostly Harmless Simulations? Using Monte Carlo Studies for Estimator Selection

We consider two recent suggestions for how to perform an empirically motivated Monte Carlo study to help select a treatment effect estimator under unconfoundedness. We show theoretically that neither is likely to be informative except under restrictive conditions that are unlikely to be satisfied in many contexts. To test empirical relevance, we also apply the approaches to a real-world setting where estimator performance is known. Both approaches are worse than random at selecting estimators which minimise absolute bias. They are better when selecting estimators that minimise mean squared error. However, using a simple bootstrap is at least as good and often better. For now researchers would be best advised to use a range of estimators and compare estimates for robustness

When Should We (Not) Interpret Linear IV Estimands as LATE?

In this paper I revisit the interpretation of the linear instrumental variables (IV) estimand as a weighted average of conditional local average treatment effects (LATEs). I focus on a practically relevant situation in which additional covariates are required for identification while the reduced-form and first-stage regressions implicitly restrict the effects of the instrument to be homogeneous, and are thus possibly misspecified. I show that the weights on some conditional LATEs are negative and the IV estimand is no longer interpretable as a causal effect under a weaker version of monotonicity, i.e. when there are compliers but no defiers at some covariate values and defiers but no compliers elsewhere. The problem of negative weights disappears in the overidentified specification of Angrist and Imbens (1995) and in an alternative method, termed "reordered IV," that I also develop. Even if all weights are positive, the IV estimand in the just identified specification is not interpretable as the unconditional LATE parameter unless the groups with different values of the instrument are roughly equal sized. I illustrate my findings in an application to causal effects of college education using the college proximity instrument. The benchmark estimates suggest that college attendance yields earnings gains of about 60 log points, which is well outside the range of estimates in the recent literature. I demonstrate that this result is driven by the existence of defiers and the presence of negative weights. Corrected estimates indicate that attending college causes earnings to be roughly 20% higher

Rural Transformations in Middle Republican Central Italy:An Archaeological Perspective

This paper explores how the sociopolitical, economic, and demographic transformations of the Middle Republican period affected rural settlement and landscape exploitation in Central Tyrrhenian Italy. Two lines of archaeological inquiry are pursued. The first concerns settlement data from three major survey projects: the South Etruria Survey, Rome Suburbium Project, and Pontine Region Project. Despite local variation, these surveys highlight two general changes firmly placed in the late 4th and 3rd centuries BC: an increase in rural site numbers and the rise of specialized commercial farms. The second topic concerns centuriation. It is argued that some field systems, including the centuriation of the Pontine plain, were laid out in the late 4th and early 3rd centuries to reclaim marginal landscapes. Labor-cost analyses suggest such projects involved substantial and sustained investment. The chapter then discusses the implications of these rural transformations in relation to urban contexts and the period’s broader history. Despite continuous warfare, Central Italy apparently witnessed demographic and economic growth, which in turn contributed to Rome’s expansion