Using latent variable models to make gaming-the-system detection robust to context variations.

Gaming the system, a behavior in which learners exploit a system's properties to make progress while avoiding learning, has frequently been shown to be associated with lower learning. However, when we applied a previously validated gaming detector across conditions in experiments with an algebra tutor, the detected gaming was not associated with reduced learning, challenging its validity in our study context. Our exploratory data analysis suggested that varying contextual factors across and within conditions contributed to this lack of association. We present a new approach, latent variable-based gaming detection (LV-GD), that controls for contextual factors and more robustly estimates student-level latent gaming tendencies. In LV-GD, a student is estimated as having a high gaming tendency if the student is detected to game more than the expected level of the population given the context. LV-GD applies a statistical model on top of an existing action-level gaming detector developed based on a typical human labeling process, without additional labeling effort. Across three datasets, we find that LV-GD consistently outperformed the original detector in validity measured by association between gaming and learning as well as reliability. LV-GD also afforded high practical utility: it more accurately revealed intervention effects on gaming, revealed a correlation between gaming and perceived competence in math and helped understand productive detected gaming behaviors. Our approach is not only useful for others wanting a cost-effective way to adapt a gaming detector to their context but is also generally applicable in creating robust behavioral measures.

An astonishing regularity in student learning rate.

Leveraging a scientific infrastructure for exploring how students learn, we have developed cognitive and statistical models of skill acquisition and used them to understand fundamental similarities and differences across learners. Our primary question was why do some students learn faster than others? Or, do they? We model data from student performance on groups of tasks that assess the same skill component and that provide follow-up instruction on student errors. Our models estimate, for both students and skills, initial correctness and learning rate, that is, the increase in correctness after each practice opportunity. We applied our models to 1.3 million observations across 27 datasets of student interactions with online practice systems in the context of elementary to college courses in math, science, and language. Despite the availability of up-front verbal instruction, like lectures and readings, students demonstrate modest initial prepractice performance, at about 65% accuracy. Despite being in the same course, students' initial performance varies substantially from about 55% correct for those in the lower half to 75% for those in the upper half. In contrast, and much to our surprise, we found students to be astonishingly similar in estimated learning rate, typically increasing by about 0.1 log odds or 2.5% in accuracy per opportunity. These findings pose a challenge for theories of learning to explain the odd combination of large variation in student initial performance and striking regularity in student learning rate.

Development and psychometric evaluation of an empirically-derived daily checklist of weight control: Consumption-reduction strategies and health-focused strategies in college students.

Objective: Many college women report engaging in weight control strategies, yet little is known about which strategies are used and how often. The current study's goal was to evaluate the factor structure of a comprehensive list of weight control behaviors used in the previous 24-hours. Participants: Undergraduate women (N = 286) were recruited from a southwestern university. Methods: Participants reported their weight control strategies for the previous 24 hours on a checklist compiled from previous studies. Results: Exploratory and confirmatory factor analyses indicated that a 14-item, 2-factor ("Consumption-reduction", "Health-focused" Strategies) structure was a good fit of the data. Tests of longitudinal measurement invariance found support for using the checklist to make meaningful comparisons across time. Conclusions: This study developed a checklist of past 24-hour weight-control strategy usage, thereby providing a step toward developing an instrument that may be used for weight control or early intervention for disordered eating.

Trauma-informed primary care for medical residents.

BACKGROUND: Psychological trauma can have a significant impact on mental and physical health, and interpersonal relationships. Many physicians report discomfort addressing psychological trauma in the context of health care visits, and few training opportunities exist for health care trainees to learn about the relationship between trauma and health. The aim of this project was to develop and implement an educational curriculum to teach medical and nursing trainees about trauma-informed primary care. METHODS: We expanded upon pilot data from a brief interdisciplinary intervention to train medical residents in trauma-informed primary care at a Veterans Affairs hospital. We generated a trauma-informed care curriculum involving five 1-hour didactic sessions, 10-minute group reflection regarding patient interactions prior to each didactic session, and optional patient care observation and feedback. The curriculum aligned with internal medicine (n = 16) and nurse practitioner (n = 5) interprofessional primary care education sessions during the 2017/18 academic year. RESULTS: The curriculum was feasible and associated with increased self-reported knowledge, attitudes and practice around trauma-informed care. Free text feedback indicated that residents found the topic important, appreciated a skills-based approach and valued experiential educational activities. CONCLUSIONS: Training residents in trauma-informed care results in improved knowledge, attitudes and practices in caring for patients with psychological trauma. Residents appreciated both experiential and skills-based exercises. Next steps include continued exploration of using direct observation and feedback, and examining effects of training on patient outcomes (e.g. satisfaction with care).

Body dissatisfaction and disordered eating in Native American, Hispanic, and White College Women.

PURPOSE: The sociocultural model of eating disorders asserts that societies which emphasize the thin-ideal have higher rates of body dissatisfaction and disordered eating. Recent research questions the related presumption that non-White cultures value a larger ideal female and thus have lower rates of body dissatisfaction and disordered eating. The limited research on these constructs in racial/ethnic minorities primarily has used non-validated instruments. The current study investigated rates of body dissatisfaction and disordered eating with validated, widely used measures. METHODS: Measures of body dissatisfaction and disordered eating were completed by 896 college women in the United States: 473 Hispanics, 341 non-Hispanic whites, and 82 Native Americans. RESULTS: Although Native Americans and Hispanics had higher body mass indices (and larger ideal shapes) than White women, the groups had similar body dissatisfaction scores. Native Americans reported somewhat less restricted eating compared to White women. When controlling for body mass index and age, group differences on body dissatisfaction emerged and the group differences in eating disorder symptoms became more pronounced, with White women showing more pathology. Reliability and validity across groups were good. CONCLUSIONS: This study offers some support for the sociocultural model of eating disorders and provides mean scores for Native American and Hispanic females on widely-used eating disorder measures. LEVEL OF EVIDENCE: Level V, cross-sectional descriptive study.

What does self-reported "dieting" mean? Evidence from a daily diary study of behavior.

Dieting is often recommended as a means of weight loss, yet research consistently shows that self-reported dieting does not result in weight loss. Toward resolving this discrepancy, this study assessed the daily dietary intake and weight control strategies of people who self-identified as dieting. College women (N = 266) provided a report of their eating pattern (dieting, "watching what I eat," and/or "eating healthy") followed by three daily diaries (24-hour recalls of dietary intake and weight control strategies) elicited on randomly selected days during a one-month period. Dieters were expected to report fewer daily calories, more daily exercise, and more daily weight control strategies than non-dieters. At baseline, 122 participants (45.9%) endorsed both "watching" and "eating healthy" ("Concerned Eaters") while 55 (20.7%) endorsed current dieting along with "watching" and "eating healthy" ("Dieters"). Just 3 (1.1%) endorsed dieting only, and 31 (11.7%) endorsed no eating pattern ("Unconcerned Eaters"). Dieters' mean BMI was in the overweight range; the mean BMIs of other groups were in the normal weight range. Dieters did not consistently endorse dieting across diaries. Nevertheless, Dieters reported fewer daily calories, and more overall weight control strategies, including more healthy weight control strategies, than Concerned Eaters. Across groups, participants' weights did not change significantly during the study. Dieters appear to engage in weight control strategies which could result in weight loss; however, their reports of whether they are dieting vary across days, suggesting a need for more consistent behavior. These results have clinical and research implications in the area of weight loss.

The role of familism in weight loss treatment for Mexican American women.

Mexican American women are disproportionately affected by overweight/obesity and the health complications accompanying them, but weight loss treatments are less successful in this ethnic group. High levels of familism, a value reflecting obligation to family that supersedes attention to oneself, interfere with weight loss for Mexican American women. This mixed methods study investigated overweight Mexican American women's beliefs about how familism, and Mexican American culture, might hinder weight loss success, and how treatments might be culturally adapted. Results suggest a need to support women in their commitment to family while also helping them make changes. Recommendations for culturally adapted treatments are made.

Data mining and education.

An emerging field of educational data mining (EDM) is building on and contributing to a wide variety of disciplines through analysis of data coming from various educational technologies. EDM researchers are addressing questions of cognition, metacognition, motivation, affect, language, social discourse, etc. using data from intelligent tutoring systems, massive open online courses, educational games and simulations, and discussion forums. The data include detailed action and timing logs of student interactions in user interfaces such as graded responses to questions or essays, steps in rich problem solving environments, games or simulations, discussion forum posts, or chat dialogs. They might also include external sensors such as eye tracking, facial expression, body movement, etc. We review how EDM has addressed the research questions that surround the psychology of learning with an emphasis on assessment, transfer of learning and model discovery, the role of affect, motivation and metacognition on learning, and analysis of language data and collaborative learning. For example, we discuss (1) how different statistical assessment methods were used in a data mining competition to improve prediction of student responses to intelligent tutor tasks, (2) how better cognitive models can be discovered from data and used to improve instruction, (3) how data-driven models of student affect can be used to focus discussion in a dialog-based tutoring system, and (4) how machine learning techniques applied to discussion data can be used to produce automated agents that support student learning as they collaborate in a chat room or a discussion board.

Mothers' and daughters' beliefs about factors affecting preadolescent girls' body satisfaction.

Body dissatisfaction is common in preadolescent girls. In this qualitative study, preadolescent girls (N=145) wrote descriptions of factors that made them feel good and bad about their bodies. Their mothers (N=145) also wrote about factors they believed made their daughters feel good and bad about their bodies. Statements were coded using thematic analysis. Chi-square analyses examined mother-daughter dyad agreement, and differences in influential factors based on ethnic identity. Despite general agreement in overall themes, results indicated limited agreement within mother-daughter dyads. Specifically, one significant result was detected: mothers and their daughters agreed on the importance of teasing as a negative influence on body satisfaction. There was one significant difference based on ethnic identity, with Hispanic girls mentioning more frequently than White girls that physical activity/exercise helped them feel good about their bodies. Recommendations are made for family-based interventions to support the body image of preadolescent girls.

Testing the measurement invariance of the Eating Disorder Inventory in nonclinical samples of Hispanic and Caucasian women.

OBJECTIVE: The factor structure of the Eating Disorder Inventory (EDI) has not been thoroughly tested in Hispanic populations, yet researchers commonly use this instrument in Hispanic samples. Thus, it is important to establish the validity of the EDI in Hispanic populations. This article investigated measurement invariance of the EDI's three eating- and weight-related (eat/wt) scales because they are the most frequently used and are often used in isolation. These scales include Drive for Thinness, Bulimia, and Body Dissatisfaction. METHOD: Female undergraduates were recruited for a study on body image. The final sample (N = 688) included participants categorized as Hispanic (N = 385) or Caucasian (N = 303). They completed the EDI-3 and a measure of acculturation. RESULTS: Measurement invariance analyses of the EDI-3 in Caucasian and Hispanic samples were conducted. The configural model provided an acceptable fit, providing support for the three-factor structure of the eat/wt scales in both the Caucasian and the Hispanic sample. However, weak invariance of the three-factor structure was not supported. When measurement invariance analyses were conducted on the three eat/wt scales separately, Drive for Thinness was the only scale to demonstrate measurement invariance. DISCUSSION: The theoretical three-factor structure of the EDI eat/wt scales was supported in both ethnic groups. Furthermore, the Drive for Thinness scale can readily be used to make group comparisons across nonclinical samples of Caucasian and Hispanic women, but researchers should be cautious when using the other two eat/wt scales to make comparisons across these two groups.

The use of real or complex coupling coefficients for lossy piezoelectric materials.

Two competing approaches for calculating coupling coefficients for lossy piezoelectric materials, one producing a real result and the other a complex result, are compared and analyzed. It is found that the complex coupling coefficient suffers from mathematical difficulties, which the real coupling coefficient does not exhibit. Moreover, it is pointed out that a prediction made by the complex coupling coefficient theory conflicts with experiment while the corresponding real coupling coefficient theory prediction does not. When a coupling coefficient of interest has been computed from the real coupling coefficient theory using piezoelectric equations having intensive independent variables, the resulting expression has the same algebraic form as the corresponding static coupling coefficient formula. Moreover, only the real parts of the piezoelectric, elastic, and dielectric material properties appear.

Full solution, for crystal class 3m, of the Holland-EerNisse complex material-constant theory of lossy piezoelectrics for harmonic time dependence.

A complex material-constant theory of lossy piezoelectrics is fully solved for crystal class 3m for harmonic time dependence of the fields and stresses. A new demonstration that the theory's eigen coupling factor equation applies to the lossy alternating current (AC) case also is given. The solution presented for crystal class 3m provides a complete orthonormal set of eigenvectors and eigenvalues for the eigen coupling factor problem, and it also provides a complete orthonormal set of eigenvectors and eigenvalues for the eigen loss tangent problem, for this crystal class. It is shown that two positive coupling factors are sufficient to express an arbitrary 3m crystal state. Despite the complex nature of the material constants, the Holland-EerNisse theory produces fully real expressions for the coupling factors. The loss tangent eigenvalues also are fully real and positive. The loss eigenstates are important because driving a crystal in a loss eigenstate tends to minimize the impact of material losses. Given also is a set of loss inequalities for crystal class 3m. The loss inequalities of crystal class 6mm are recovered from these when d22 and s(E)14 both vanish.

Mechanical and electromechanical properties of PMNT single crystals for naval sonar transducers.

PMNT single crystals in the relaxor-ferroelectric lead magnesium niobate (PMN)-lead titanate (PT) system provide significant advantage for underwater sonar transducers. Compared to lead zirconate titanate (PZT) ceramics, the large electromechanical coupling factor provides significant increases in transducer bandwidth. The superior strain energy density generates higher source level across the band, and the lower Young's modulus allows considerably smaller transducers. These payoffs occur even when PMNT crystals are subject to navy operating conditions such as uniaxial mechanical compressive stresses up to 42 MPa, electric fields up to 1.2 MV/m, and a temperature range from 5 to 50 degrees C. The impact of navy-relevant electric fields and mechanical stresses on crack propagation and failure of piezoelectric single crystals is investigated. The compressive, flexural, and tensile strength of PMNT crystals is reported and discussed with respect to conventional PZT ceramics and the operating conditions of a typical naval transducer.

Generalization of a model of hysteresis for dynamical systems.

A previously described model of hysteresis [J. C. Piquette and S. E. Forsythe, J. Acoust. Soc. Am. 106, 3317-3327 (1999); 106, 3328-3334 (1999)] is generalized to apply to a dynamical system. The original model produces theoretical hysteresis loops that agree well with laboratory measurements acquired under quasi-static conditions. The loops are produced using three-dimensional rotation matrices. An iterative procedure, which allows the model to be applied to a dynamical system, is introduced here. It is shown that, unlike the quasi-static case, self-crossing of the loops is a realistic possibility when inertia and viscous friction are taken into account.