A statistical model of tracking

A method is proposed to model individual patterns of growth over time by linear combinations of optimally chosen weighted orthogonal vectors. The goal is to distinguish individuals who track from nontrackers. Nontrackers are defined as those who follow different, usually more complex, growth patterns than trackers. Thus, nontrackers require more vectors than do trackers in modeling their longitudinal observations. A method of specifying the class-specific vectors and individual weights is demonstrated. When the proportion of nontrackers in the population is small, a modified form of the Akaike maximum entropy criterion is used to select the number of vectors appopriate for each person and also to classify each person into a tracking category. When the proportion of nontrackers is large, the modified Akaike criterion together with scatterplots of the growth curve weights are needed to distinguish trackers from nontrackers. The apprach is illustrated with longitudinal observations of height measured in an epidemiologic survey of children.     

Confidence limits for estimates of totals from stratified samples, with application to medicare Part B overpayment audits

Superpopulation models are proposed that should be appropriate for modelling sample-based audits of Medicare payments and other overpayment situations. Simulations are used to estimate the coverage probabilities of confidence intervals formed using the standard Stratified Expansion and Combined Ratio estimators of the total. Despite severe departures from the usual model of normal deviations, these methods have actual coverage probabilities reasonably close to the nominal level specified by the US government's sampling guidelines. An exception occurs when all claims from a single sampling unit are either completely allowed, or completely denied, and for this situation an alternative is explored. A balanced sampling design is also examined, but shown to make no improvement over ordinary stratified samples used in conjunction with ratio estimates.     

Obesity-related behaviors in adolescent friendship networks

This study examines obesity-related behaviors within adolescent friendship networks, because adolescent peers have been identified as being important determinants of many health behaviors. We applied ERGM selection models for single network observations to determine if close adolescent friends engage in similar behaviors and to explore associations between behavior and popularity. Same-sex friends were found to be similar on measures of organized physical activity in two out of three school-based friendship networks. Female friends were found to engage in similar screen-based behaviors, and male friends tended to be similar in their consumption of high-calorie foods. Popularity (receiving ties) was also associated with some behaviors, although these effects were gender specific and differed across networks.     

Sexual functioning and practices in a multi-ethnic study of midlife women: baseline results from SWAN

This study examined the sexual practices and function of midlife women by ethnicity (African American, Caucasian, Chinese, Hispanic, Japanese) and menopausal status. Sexual behavior was compared in 3,262 women in the baseline cohort of SWAN. Participants were 42 to 52 years old, premenopausal or early perimenopausal, and not hysterectomized or using hormones. Analysis used multivariate proportional odds regression. In our sample, 79% had engaged in sex with a partner in the last 6 months, and a third considered sex to be very important. Common reasons for no sex (n = 676) were lack of partner (67%), lack of interest (33%), and fatigue (16%). Compared with Caucasians, Japanese and Chinese women were less likely, and African Americans more likely, to report sex as very important (p < 0.005). Significant ethnic differences were found for frequency of all practices. Perimenopause status was associated only with higher frequencies of masturbation and pain during intercourse.     

Bipolar disorder in children

This article presents an overview of bipolar disorder (BPD) in children, a condition that only recently has been recognized as a legitimate diagnosis. Bipolar disorder in children is underrecognized for many reasons including lack of awareness, diagnostic confusion, and the different clinical picture in children. Available data strongly suggest that prepubertal childhood BPD is a non-episodic, chronic, rapid cycling, mixed manic state. It may be comorbid with attention-deficit/hyperactivity disorder (ADHD) and conduct disorder (CD) or it may demonstrate features of ADHD and CD, further complicating recognition and subsequent treatment. Treatment issues are discussed, and some reasons for the urgency of early recognition and treatment are explained.     

Sectors of activity, topography, and parasitism in home areas of New Guinea coarse-haired rats, and Trombiculidae (Acarina)

Summary Home areas of hosts are, in effect the gardens in which parasite populations grow. The parasites flourish in response to the kind and amount of host activity modified, of course, by the habitat, and become microcommunities supported by their host and its artifacts. When scatter diagrams of points at which hosts have been observed are divided by median major and minor axes, and when the resulting four quarters, designated A, B, C, D, corresponding to concentration of points in the quarters, the relative concentration usually is: A>B>C>D. The concentration of observed points also is generally greatest nearest the major axis and frequently, but not always, near the median center. Nests of hosts, hence nest-parasites, appear generally to be near the center. For the host examined in detail here, the New Guinea coarse-haired rat, mostLeptotrombidium deliensis appear to have been acquired in the AB sector of the host's home areas but a greater diversity of chiggers is acquired in the CD sector. It is postulated that, ifL. akamushi had been present, it would have occurred in the CD sector where, though the observed concentration of host activity was least, the mixed grassforb and shrub habitat would have been more suitable than in the AB sector.Gahrliepia pingue, C. ewingi, Schoengastia blestowei andS. schueffneri, appear also to be more abundant in the CD sector than in the AB sector. The chiggers themselves have home clusters, or lairs, and adjacent areas of activity (home areas) somewhat resembling those of the hosts. This analysis of sectors of home areas was begun in 1965 under provision of a research grant (AI-03653) by the National Institutes of Health to the Division of Parasitology, University of California at Berkeley. It was completed during 1967.