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In this paper we propose a variance estimator for the OLS estimator as well as for nonlin-ear estimators such as logit, probit and GMM. This variance estimator enables cluster-robust inference when there is two-way or multi-way clustering that is non-nested. The variance esti-mator extends the standard cluster-robust variance estimator or sandwich estimator(More)
We consider statistical inference for regression when data are grouped into clusters , with regression model errors independent across clusters but correlated within clusters. Examples include data on individuals with clustering on village or region or other category such as industry, and state-year dierences-in-diierences studies with clustering on state.(More)
Diagnostic ultrasound contrast agents have been developed for enhancing the echogenicity of blood and for delineating other structures of the body. Approved agents are suspensions of gas bodies (stabilized microbubbles), which have been designed for persistence in the circulation and strong echo return for imaging. The interaction of ultrasound pulses with(More)
In this paper we survey methods to control for regression model error that is correlated within groups or clusters, but is uncorrelated across groups or clusters. Then failure to control for the clustering can lead to understatement of standard errors and overstatement of statistical significance, as emphasized most notably in empirical studies by Moulton(More)
In this paper we consider inference with paired or dyadic data, such as cross-section and panel data on trade between two countries. Regression models with such data have a complicated pattern of error correlation. For example, errors for US-UK trade may be correlated with those for any other country pair that includes either the US or UK. We consider(More)
BACKGROUND Myocardial cavitation-enabled therapy (MCET) has been proposed as a means to achieve minimally invasive myocardial reduction using ultrasound to produce scattered microlesions by cavitating contrast agent microbubbles. METHODS Rats were treated using burst mode focused ultrasound at 1.5 MHz center frequency and varying envelope and pressure(More)
BACKGROUND High-intensity ultrasound pulses intermittently triggered from an ECG signal can interact with circulating contrast agent microbubbles to produce myocardial cavitation microlesions of potential therapeutic value. In this study, the timing of therapy pulses relative to the ECG R wave was investigated to identify the optimal time point for tissue(More)