Susan J. Henly

MODEL SELECTION IN COVARIANCE STRUCTURES ANALYSIS AND THE PROBLEM OF SAMPLE SIZE : A CLARIFICATION

Complex models for covariance matrices are structures that specify many parameters, whereas simple models require only a few. When a set of models of differing complexity is evaluated by means of some goodness of fit indices, structures with many parameters are more likely to be selected when the number of observations is large, regardless of other utility considerations. This is known as the sample size problem in model selection decisions. This article argues that this influence of sample size is not necessarily undesirable. The rationale behind this point of view is described in terms of the relationships among the population covariance matrix and 2 model-based estimates of it. The implications of these relationships for practical use are discussed.

Factors associated with very early weaning among primiparas intending to breastfeed.

Objectives: The major objective of this study was to identify predictor variables that accurately differentiated breastfeeding women who weaned during the first 4 weeks, those who weaned between 5 and 26 weeks, and those who weaned after 26 weeks. Predictors were demographic variables, Theory of Planned Behavior (TPB) variables, breastfeeding knowledge, and difficulties experienced during the first month. Methods: Primiparas who delivered healthy infants in an urban midwestern hospital provided initial data prior to discharge. Follow-up occurred at 1,3,6,9, and 12 months. Following appropriate bivariate analyses, polychotomous logistic regression was used to determine predictors of weaning group. Linear multiple regression was used to predict intended duration. Results: Most of the 84 women who weaned very early had intended to breastfeed considerably longer. According to the multivariate analysis, women who weaned earlier were younger, had completed fewer years of education, had a more positive bottle-feeding attitude and a less positive breastfeeding attitude, intended to breastfeed less time, had lower knowledge scores, had higher perceived insufficient milk scores, and planned to work outside the home. Variables postulated by the TPB to be direct predictors of intention explained 36% of the variance in intended duration. Conclusions: Women at risk for early weaning can be identified with reasonable accuracy using a TPB-based conceptual framework expanded to include breastfeeding specific variables. Casefinding using empirically derived screening methods and careful postpartum follow-up, along with professional intervention, should be used to avert unintended early weaning.

A realistic perspective on pattern representation in growth data: Comment on Bauer and Curran (2003)

D. J. Bauer and P. J. Curran (2003) cautioned that results obtained from growth mixture models may sometimes be inaccurate. The problem they addressed occurs when a growth mixture model is applied to a single, general population of individuals but findings incorrectly support the conclusion that there are 2 subpopulations. In an artificial sampling experiment, they showed that this can occur when the variables in the population have a nonnormal distribution. A realistic perspective is that although a healthy skepticism to complex statistical results is appropriate, there are no true models to discover. Consequently, the issue of model misspecification is irrelevant in practical terms. The purpose of a mathematical model is to summarize data, to formalize the dynamics of a behavioral process, and to make predictions. All of this is scientifically valuable and can be accomplished with a carefully developed model, even though the model is false.

Social Connections, Trajectories of Hopelessness, and Serious Violence in Impoverished Urban Youth.

Youth living in impoverished urban neighborhoods are at risk for becoming hopeless about their future and engaging in violent behaviors. The current study seeks to examine the longitudinal relationship between social connections, hopelessness trajectories, and subsequent violent behavior across adolescence. Our sample included 723 (49% female) African American youth living in impoverished urban neighborhoods who participated in the Mobile Youth Survey from 1998 through 2006. Using general growth mixture modeling, we found two hopelessness trajectory classes for both boys and girls during middle adolescence: a consistently low hopelessness class and an increasingly hopeless class with quadratic change. In all classes, youth who reported stronger early adolescent connections to their mothers were less hopeless at age 13. The probability of later adolescent violence with a weapon was higher for boys and was associated with the increasingly hopeless class for both boys and girls. Implications for new avenues of research and design of hope-based prevention interventions will be discussed.

Physical Activity in Women Receiving Chemotherapy for Breast Cancer: Adherence to a Walking Intervention

PURPOSE/OBJECTIVES To describe and predict adherence to a physical activity protocol for patients with breast cancer receiving chemotherapy. DESIGN Longitudinal, observational study. SETTING Cancer center in the upper Midwestern region of the United States. SAMPLE 36 patients with breast cancer aged 40-55 years who were receiving adjuvant treatment. METHODS A longitudinal study was conducted within a randomized clinical trial comparing the effects of physical activity versus bisphosphonates on bone mineral density. Participants randomized to physical activity were advised to walk 10,000 steps per day and received initial physical therapy consultation and ongoing motivational interviewing. Multilevel modeling was used to identify variables that predict adherence. MAIN RESEARCH VARIABLES Adherence to the 10,000-step protocol was estimated with total steps and mean steps per day. FINDINGS Thirty-six women were enrolled in the physical activity group; 29 provided step data. The mean total steps per participant for the first six weeks was 280,571 (SD = 111,992), which is 67% of the prescribed steps. Excluding days when no steps were recorded, the mean steps per day for the initial six-week period was 7,363 (SD = 2,421), a 74% adherence rate. A significant linear increase occurred in steps per day after chemotherapy in a treatment cycle (p < 0.0001). Baseline inactivity predicted adherence. CONCLUSIONS Adherence to the walking program was compromised during chemotherapy but improved after chemotherapy completion. IMPLICATIONS FOR NURSING Knowing that chemotherapy predicts adherence to a walking protocol is useful for selecting the type, timing, and intensity of physical activity interventions.

Bullying (ijime) among Japanese hospital nurses: modeling responses to the revised Negative Acts Questionnaire.

Background:Workplace bullying interferes with provision of optimal care to patients and contributes to decreased job satisfaction and withdrawal of nurses from the workforce. Little is known about bullying (ijime) or its measurement among Japanese hospital nurses. Objectives:The objectives of this study were to describe responses and explore dimensionality of a Japanese translation of the 23-item revised Negative Acts Questionnaire (NAQ-R), a frequently used measure of bullying. Method:Responses of 881 registered nurses working in hospitals in Japan who answered all 23 NAQ-R items were analyzed. Descriptive statistics were used to summarize item responses, the principal components analysis approaches used by other international investigators were replicated, and five exploratory maximum likelihood factor analysis models were estimated. Results:Responses to the 5-point (1 = never to 5 = daily) NAQ-R items were skewed, and 19% of the nurses replied never to all 23 items. The principal components analysis produced three components with eigenvalues greater than 1, and all five maximum likelihood exploratory factor analytic models were rejected using the chi-square test statistic. Model comparison based on the Akaike Information Criterion identified the five-factor maximum likelihood model as the best approximating structure. Discussion:Dimensionality of the NAQ-R item set included verbal bullying, physical bullying, exploitation, undervaluation, and isolation. The solution reflected experiences of bullying reported in international studies, unique characteristics of Japanese bullying, and skewness in the data. Item response theory is recommended as an alternative way to gain insight into item functioning when the NAQ or its translations are used to measure nursing workplace bullying.

The notion of time in symptom experiences.

BackgroundThe experience of unpleasant sensations associated with the presence of symptoms prompts self-care or help seeking to obtain explanations for the symptoms, manage emotional responses, or obtain treatment for symptom alleviation and elimination. ObjectiveThe purpose of this article is to summarize and comment on three existing symptom theories, with special attention to temporal factors. MethodsExisting theories are synthesized as the time dimensions of symptom experiences and symptom management processes are elucidated. Clinical examples and findings from empirical studies illustrate critical points. DiscussionExisting theories describing the symptom experience and the process of symptom management refer implicitly to the role of time or use limited dimensions of time. Symptom experiences in time (SET) theory is proposed as a synthesis and extension of existing theories. The SET theory conceives the symptom experience as a flow process that explicitly incorporates temporal dimensions. Four dimensions of time are recognized: clock-calendar, biologic-social, perceived, and transcendent time. The four temporal dimensions are placed against a backdrop of “meaning-in-time” that brings forth the potential for transformation in a symptom experience. Increasing sophistication in design, measurement, and data analysis is required to test and evaluate SET theory-based propositions. ConclusionsThe SET theory extends previous work by incorporating multiple temporal dimensions that reflect the human experience of health and illness manifested in the expression and management of symptoms.

Health and illness over time: The trajectory perspective in nursing science

BACKGROUND Understanding change in health and illness over time is central to creating and evaluating interventions for individuals, families, and populations. The term health trajectory is a succinct and useful way to describe change in health status over time. OBJECTIVES The aims of this article were to define the notion of a health trajectory; comment on the usefulness and current status of health trajectory research for nursing science and practice; and identify and illustrate the key elements of theory, design, and statistical models for health trajectory research. APPROACH Constructs in theory about individual change are summarized, synthesized with characteristics of longitudinal design and statistical models for change, and discussed in light of current and emerging health care priorities and trends in nursing research. RECOMMENDATIONS Health trajectory research is person focused and congruent with the person-centered emphasis of nursing practice. The contribution of nursing science to the overall effort to improve health will be enhanced when change over time is explicit in nursing theory, longitudinal designs are used, and contemporary statistical approaches for modeling change in health status are incorporated into research plans.

Clinical measurement of limb spasticity in adults: state of the science.

ABSTRACT Spasticity is a neuromuscular dysfunction characterized by tight or stiff muscles. Spasticity occurs across the spectrum of upper motor neuron disease and complicates the course and quality of life of those affected. Accurate and precise assessment of spasticity is the first step in providing safe and effective treatments to patients for management of spasticity. Examiner evaluations (Ashworth Scale, Modified Ashworth, and Visual Analog Scale) and patient self-reports (Visual Analog Scale and Numeric Rating Scale) are used to assess spasticity in clinical practice. We reviewed the biology of spasticity and summarized research that assessed properties of scores obtained from clinical scales when used in a variety of upper motor neuron diseases. The definition of spasticity was inconsistent. Rater reliability or agreement on clinical scales varied widely. Correspondence with electromyogram results was mixed. There was dissimilarity in patient reports and examiner assessments. Scores from clinical scales are responsive (decrease after initiation of treatment with known effectiveness), but the utility of scores for indexing individual change associated with the natural history of upper motor neuron disease is unknown. Future research incorporating patient reports and examiner findings over time will help to clarify the definition and capture the essence of spasticity.

Professionally Mediated Peer Support and Early Breastfeeding Success

Social support interventions that incorporate professionally mediated peer support (PMPS) for improved breastfeeding outcomes were compared with no special breastfeeding support. Fifty-five breastfeeding mothers participated. The breastfeeding outcomes of duration, completeness, satisfaction, and exclusive breastfeeding were compared at 6 weeks postpartum among an experimental group that received PMPS, and among younger community (YC) and older community (OC) groups that received no special breastfeeding support. The PMPS group exclusively breastfed for a significantly longer duration than the YC group. At 6 weeks, mothers in both community groups who had weaned were significantly less satisfied with their breastfeeding experiences than the mothers who were still nursing their babies. Professionally mediated peer support can improve the early breastfeeding outcomes of duration of exclusive breastfeeding and satisfaction with breastfeeding.