Quality of life as a mediator of leisure activity and perceived health among older women

Despite consistent evidence to suggest that participating in leisure is associated with perceived health status among older adults, there have been few attempts to determine the possible underlying mechanisms in this relationship, including the role of quality of life (QoL). This study examined the role of perceived quality of life in the relationship between leisure and perceived health in older women. Correlations, regression, and mediation analysis were conducted on data from the Woman’s College Alumnae Women’s Health Study. Results indicate that QoL partially mediates the relationship between leisure and perceived health in older women. Findings further establish the link between leisure and perceived health with QoL playing an important role in the relationship.     

An empirical saddlepoint approximation based method for smoothing survival functions under right censoring

The Kaplan–Meier (KM) estimator is ubiquitously used for estimating survival functions, but it provides only a discrete approximation at the observation times and does not deliver a proper distribution if the largest observation is censored. Using KM as a starting point, we devise an empirical saddlepoint approximation‐based method for producing a smooth survival function that is unencumbered by choice of tuning parameters. The procedure inverts the moment generating function (MGF) defined through a Riemann–Stieltjes integral with respect to an underlying mixed probability measure consisting of the discrete KM mass function weights and an absolutely continuous exponential right‐tail completion. Uniform consistency, and weak and strong convergence results are established for the resulting MGF and its derivatives, thus validating their usage as inputs into the saddlepoint routines. Relevant asymptotic results are also derived for the density and distribution function estimates. The performance of the resulting survival approximations is examined in simulation studies, which demonstrate a favourable comparison with the log spline method (Kooperberg & Stone, 1992) in small sample settings. For smoothing survival functions we argue that the methodology has no immediate competitors in its class, and we illustrate its application on several real data sets. The Canadian Journal of Statistics 47: 238–261; 2019 © 2019 Statistical Society of Canada     

A Twin Study of Objective and Subjective Pubertal Timing and Peer Influence on Risk‐Taking

This study used a behavioral genetic design to test whether three measures of pubertal timing moderated peer influence on risk‐taking in a sample of 248 female adolescent twin pairs (M_age = 16.0, SD = 1.5) from the National Longitudinal Study of Adolescent Health. Peer influence was operationalized as the quasi‐causal association between girls' self‐reported risk‐taking and the risk‐taking reported by their friends. Girls with earlier ages at menarche and who perceived themselves as more developed than peers were more susceptible to peer influence on risk‐taking. However, age‐standardized ratings of body changes did not moderate peer influence. This study highlights distinctions between multiple measures of pubertal timing, using an innovative synthesis of genetically informative data and peer nomination data.     

Cold-related injuries in a cohort of homeless adults

People experiencing homelessness have an increased risk of cold-related injuries. This study determined the rate of emergency department (ED) visits for cold-related injuries among homeless adults and low-income controls in Toronto, Canada. Homeless individuals were recruited at shelters and meal programs. Age- and sex-matched controls living in low-income neighborhoods were selected. ED utilization was ascertained over 4-years of follow-up (2005–9) using administrative databases. A total of 16 ED visits for cold-related injuries were observed among 587 homeless men and 296 homeless women. The rate of ED visits was 6.7 (95% CI, 4.2–12.4) per 1000 person-years of observation among homeless men and 0.9 (95% CI, 0.03–5.6) among homeless women. ED visit rates were significantly higher among homeless men compared to low-income men (P?<?0.001) and significantly higher among homeless men compared to homeless women (P?=?0.03). Targeted public health interventions are needed to reduce the risk of cold-related injuries among people experiencing homelessness.     

Towards a critical realist epistemology?

When critical realists consider epistemology they typically start from “epistemological relativism.” We find this position necessary, but we also find it insufficient because it lacks a critique of the highly unequal social relations among observers themselves—relations that shape the very production of knowledge. While it is indeed the case that all knowledge is fallible, it is also the case that all knowledge is positioned, with a particular standpoint. What is more, the social power relations between standpoints organize the production of truth in ways that produce systematic distortions. In this paper, we propose a critical realist social epistemology. We introduce feminist standpoint theory and postcolonial theory as our suggested interventions into critical realism and we use two case studies of existing work to highlight i) the social production of truth and the real, and ii) what is at stake for radicalizing epistemology in critical realism. In so doing, our paper emphasizes the epistemic complexities that continuously shape ontology, a commitment to subaltern voices or experiences, and a thorough interrogation of the relations between positions of knowledge production.     

How College Students Spend Their Time Communicating

This study sought to assess how college students spend their time communicating and what impact, if any, communications devices may be having on how that time is spent. Undergraduates (N=696) at four southeastern colleges were surveyed. Results revealed that listening comprises 55.4% of the total average communication day followed by reading (17.1%), speaking (16.1%), and writing (11.4%). Each of these communication behaviors includes some aspect of Internet use. College students spend as much time listening to media as they do engaged in interpersonal interactions. New technology is changing the way mediated communication activities are perceived. A different paradigm of expressive, receptive, and interactive communication is offered.     

Analytic expressions for maximum likelihood estimators in a nonparametric model of tumor incidence and death

This research focuses on the estimation of tumor incidence rates from long-term animal studies which incorporate interim sacrifices. A nonparametric stochastic model is described with transition rates between states corresponding to the tumor incidence rate, the overall death rate, and the death rate for tumor-free animals. Exact analytic solutions for the maximum likelihood estimators of the hazard rates are presented, and their application to data from a long-term animal study is illustrated by an example. Unlike many common methods for estimation and comparison of tumor incidence rates among treatment groups, the estimators derived in this paper require no assumptions regarding tumor lethality or treatment lethality. The small sample operating characteristics of these estimators are evaluated using Monte Carlo simulation studies.     

Practical small sample inference for single lag subset autoregressive models

We propose a method for saddlepoint approximating the distribution of estimators in single lag subset autoregressive models of order one. By viewing the estimator as the root of an appropriate estimating equation, the approach circumvents the difficulty inherent in more standard methods that require an explicit expression for the estimator to be available. Plots of the densities reveal that the distributions of the Burg and maximum likelihood estimators are nearly identical. We show that one possible reason for this is the fact that Burg enjoys the property of estimation equation optimality among a class of estimators expressible as a ratio of quadratic forms in normal random variables, which includes Yule–Walker and least squares. By inverting a two-sided hypothesis test, we show how small sample confidence intervals for the parameters can be constructed from the saddlepoint approximations. Simulation studies reveal that the resulting intervals generally outperform traditional ones based on asymptotics and have good robustness properties with respect to heavy-tailed and skewed innovations. The applicability of the models is illustrated by analyzing a longitudinal data set in a novel manner.