V. S. Ramakrishnan

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BACKGROUND Several recent studies have found a higher lifetime prevalence of suicide attempts in homosexual males compared with heterosexual control subjects or population rates. These studies used either convenience samples, most without controls, or population-based samples in which confounding factors such as depression and substance abuse were not(More)
We consider the problem of characterizing the minimum of a submodular function when the minimization is restricted to a family of subsets. We show that, for many interesting cases, there exist two elements a and b of the groundset such that the problem is equivalent to the problem of minimizing the submodular function over the sets containing a but not b.(More)
This twin study estimates familial clustering of moderate and intense leisure-time physical activity and investigates quantitatively its genetic and environmental components. Study subjects are 3,344 male twin pairs aged 33-51 yr. Moderate activity levels were assessed with six questions about discretionary walking or stair climbing for exercise. Five(More)
Genetic and environmental influences on insomnia were studied in 2,825 pairs of Vietnam era veteran male twins. The self-reported sleep problems studied included trouble falling asleep, trouble staying asleep, waking often, waking tired and a composite sleep scale. Twin correlations for each of the sleep problems were larger in monozygotic than in dizygotic(More)
This paper presents an elementary statistical method for analyzing dichotomous outcomes in unselected samples of twin pairs using stratified estimators of the odds ratio. The methodology begins by first randomly designating one member of each twin pair as an "index" twin and the other member as the "co-twin." Stratifying on zygosity, odds ratios are used to(More)
In this paper we develop a methodology for the identification of large numbers of U.S. adult twin pairs. Data for this study derive from the U.S. Department of Defense and the Vietnam Era Twin (VET) Registry. The Department of Defense identified potential male twins (n = 10,002) using a computerized record linkage algorithm based on the same last name, same(More)
We present frequency and spatial adaptive packet wavelet coder implemented with Cellular Neural Network architecture. This paper also demonstrates how the cellular neural universal machine (CNNUM) architecture can be extended to image compression. The packet wavelet coder performs the operation of image compression, aided by CNN architecture. It uses the(More)
In this paper, a method with which to identify a national cohort of elderly twins is proposed. Record linkage algorithms were developed and applied to the > 30 million records contained in the Medicare beneficiary file. The matching algorithm for male/male pairs used race (black or white), last name, date of birth, and state of issuance of the Social(More)
The univariate analysis of categorical twin data can be performed using either structural equation modeling (SEM) or logistic regression. This paper presents a comparison between these two methods using a simulation study. Dichotomous and ordinal (three category) twin data are simulated under two different sample sizes (1,000 and 2,000 twin pairs) and(More)