We consider statistical inference for regression when data are grouped into clusters, with
regression model errors independent across clusters but correlated within clusters. Examples …

Researchers have increasingly realized the need to account for within-group dependence
in estimating standard errors of regression parameter estimates. The usual solution is to …

In this article we propose a variance estimator for the OLS estimator as well as for nonlinear
estimators such as logit, probit, and GMM. This variance estimator enables cluster-robust …

This paper exploits a new source of variation in Head Start funding to identify the program's
effects on health and schooling. In 1965 the Office of Economic Opportunity (OEO) provided …

Applications of ultrasound in medicine for therapeutic purposes have been accepted and
beneficial uses of ultrasonic biological effects for many years. Low‐power ultrasound of about …

In this paper, we examine how business cycles affect labor market outcomes in the United
States. We conduct a detailed analysis of how cycles affect outcomes differentially across …

This selective review of the biological effects of ultrasound presents a synopsis of our current
understanding of how cells insonated in vitro are affected by inertial cavitation from the …

Cultured Chinese hamster ovary cells were exposed to 2.25-MHz ultrasound in sterile 4.5-mL
polyethylene chambers and tested for cell lysis, sonoporation and DNA transfection. Ten …

A phase shift droplet emulsion is introduced as an aid to unusual ultrasound (US) applications.
The transpulmonary droplet emulsion (90% < 6 μm diameter) is made by mixing saline, …

Abstract Development of nonviral gene transfer methods would be a valuable addition to the
gene-therapy armamentarium, particularly for localized targeting of specific tissue volumes. …