Sophie Yu-Pu Chen

Research Summary: Strategic management has seen numerous studies analyzing interaction terms in nonlinear models since Hoetker's ( Strat Mgmt J. , 2007, 28 (4), 331–343) best‐practice recommendations and Zelner's ( Strat Mgmt J., 2009, 30 (12), 1335–1348) simulation‐based approach. We suggest an alternative recentering approach to assess the statistical and economic importance of interaction terms in nonlinear models. Our approach does not rely on making assumptions about the values of the control variables; it takes the existing model and data as is and requires fewer computational steps. The recentering approach not only provides a consistent answer about statistical meaningfulness of the interaction term at a given point of interest, but also helps to assess the effect size using the template that we offer in this study. We demonstrate how to implement our approach and discuss the implications for strategy researchers. Managerial Summary: In industry settings, the relationship between multiple corporate strategy‐related inputs and corporate performance is often nonlinear in nature. Furthermore, such relationships tend to vary for different types of firms represented within the broader population of firms in a given industry. It is thus imperative for managers to know how to take nonlinear relationships between related business factors into account when they make strategic decisions. We suggest a simple and easily implementable way of assessing and interpreting interactions in a nonlinear setting, which we term a recentering approach. We demonstrate how to apply our approach to a strategic management setting.

Stress reduction through contact with nature is well established, but far less is known about the contribution of contact parameters – duration, frequency, and nature quality. This study describes the relationship between duration of a nature experience (NE), and changes in two physiological biomarkers of stress – salivary cortisol and alpha-amylase. It is the first study to employ long-term, repeated-measure assessment and the first evaluation wherein study participants are free to choose the time of day, duration, and the place of a NE in response to personal preference and changing daily schedules. During an 8-week study period, 36 urban dwellers were asked to have a NE, defined as spending time in an outdoor place that brings a sense of contact with nature, at least three times a week for a duration of 10 min or more. Their goal was compliance within the context of unpredictable opportunity for taking a nature pill. Participants provided saliva samples before and after a NE at four points over the study period. Before-NE samples established the diurnal trajectory of each stress indicator and these were in line with published outcomes of more closely controlled experiments. For salivary cortisol, an NE produced a 21.3%/hour drop beyond that of the hormone’s 11.7% diurnal drop. The efficiency of a nature pill per time expended was greatest between 20 and 30 min, after which benefits continued to accrue, but at a reduced rate. For salivary alpha-amylase, there was a 28.1%/h drop after adjusting for its diurnal rise of 3.5%/h, but only for participants that were least active sitting or sitting with some walking. Activity type did not influence cortisol response. The methods for this adaptive management study of nature-based restoration break new ground in addressing some complexities of measuring an effective nature dose in the context of normal daily life, while bypassing the limitations of a clinical pharmacology dose–response study. The results provide a validated starting point for healthcare practitioners prescribing a nature pill to those in their care. This line of inquiry is timely in light of expanding urbanization and rising healthcare costs.

In randomized controlled trials with delayed treatment effect, there is a delay period before the experimental therapy starts to exhibit a beneficial effect. The phenomenon of delayed treatment effect is often observed in the emerging and important field of immuno-oncology. It is important to estimate the duration of delay as this information helps in characterizing the pattern of comparative treatment effect, understanding the mechanism of action of the experimental therapy, and forming optimal treatment strategies. For a fixed delay time, we propose a maximum likelihood estimator and evaluate its asymptotic properties via simulation. We further evaluate two functions that link the pre- and postdelay hazard ratios to the average hazard ratio given a fixed delay time. For the case of random delay time, where the delay time may vary from patient to patient, we propose a semiparametric joint survival model for delay time and event time to estimate the mean delay time and the postdelay hazard ratio, assuming a Beta distribution for the delay time. We describe an extension of the model to estimate subgroup-specific mean delay times. Simulation study and application to data from a clinical trial in colon cancer patients demonstrate the robustness of the proposed model.

Context: The role of the extracellular matrix (ECM) in regulating adipocyte metabolism in the context of metabolic disease is poorly defined. Objective: The objective of this study was to define the metabolic phenotype of adipocytes associated with human diabetes (DM) and the role of the ECM in regulating adipocyte metabolism. Design: Adipose tissues from obese patients were studied in standard 2-dimensional (2D) cell culture and an in vitro model of decellularized adipose tissue ECM repopulated with human adipocytes, and results were correlated with DM status. Setting: This study was conducted at the Academic University Medical Center and Veteran’s Administration Hospital. Patients: Seventy patients with morbid obesity undergoing bariatric surgery were included in the study. Interventions: Visceral and subcutaneous adipose tissues were collected at the time of bariatric surgery. Outcome measures: This study used metabolic assays for glucose uptake, lipolysis, and lipogenesis in adipocytes in 2D cell culture and 3-dimensional ECM culture. Results: Adipocytes from subjects with DM manifest decreased glucose uptake and decreased lipolysis in 2D culture. ECM supports differentiation of mature adipocytes and recapitulates DM-specific differences in adipocyte metabolism observed in 2D culture. ECM from subjects without DM partially rescues glucose uptake and lipolytic defects in adipocytes from subjects with DM, whereas ECM from subjects with DM impairs glucose uptake in adipocytes from subjects without DM. Conclusions: DM is associated with adipocyte metabolic dysfunction. The ECM regulates adipocyte metabolism. Nondiabetic ECM rescues metabolic dysfunction in DM adipocytes, whereas DM ECM imparts features of metabolic dysfunction to nondiabetic adipocytes. These findings suggest the ECM as a target for manipulating adipose tissue metabolism.

Summary: Background: Temperament is associated with obesity risk. However, the mechanisms linking temperament and eating behaviour to childhood adiposity are unclear.Objectives: To examine whether three temperament dimensions (surgency, effortful control and negative lability) are uniquely associated with an increased BMI z score (BMIz) concurrently and an excessive rate of change in BMIz longitudinally through four eating behaviours (food responsiveness, enjoyment of food, emotional overeating and satiety responsiveness) among low‐income pre‐schoolers, independent of home environment quality.Methods: 379 pre‐schoolers were recruited from Head Start in the Midwest region of the United States. Primary caregivers reported child temperament, eating behaviours and the level of chaos at home. Child BMIz was derived from weight and height measurements at ages 4, 5 and 6 years on average.Results: Path analyses revealed that higher levels of surgency predicted more food responsiveness and enjoyment of food, which was in turn associated with higher concurrent BMIz, independent of effortful control, negative lability and home chaos.Conclusion: Low‐income surgent pre‐schoolers were more likely to have elevated BMIz as they were more inclined to eat in response to external cues and have a high appetitive drive. Obesity prevention programmes might target low‐income children with surgent temperaments, and the identified eating behaviours.

This study examined sleep hygiene practices and bedtime resistance and tested whether associations differed by child temperament. Parents of Head Start preschoolers (n = 374, 56% non-Hispanic white) completed the Going to Bed subscale of the Children's Sleep-Wake Scale (GTB; higher score reflects less bedtime resistance), Children's Sleep Hygiene Scale (CSHS; higher score reflects better sleep hygiene), and Child Behavior Questionnaire (Anger, Activity, Impulsivity subscales indicated difficult temperament). Monte Carlo simulation adjusted for demographic covariates tested associations of CSHS with GTB in children with more- vs. less-difficult temperaments. Children with more- vs. less-difficult temperaments experienced worse sleep hygiene (p < .0001) and had more bedtime resistance (p < .0001). Among children with more difficult temperaments, better sleep hygiene was linearly associated with less bedtime resistance (β = 1.28, 95% CI 0.77, 1.78). Among children with less difficult temperaments, the association followed a piecewise linear trend: sleep hygiene was not associated with bedtime resistance when CSHS scores were < 4.1 (β = 0.15, 95% CI −4.87, 3.13), but for CSHS scores ≥ 4.1, an increase in CSHS was associated with lower bedtime resistance (β = 1.33, 95% CI 1.00, 1.79). Consistent sleep hygiene is associated with less bedtime resistance and may be helpful in reducing bedtime resistance among children with more difficult temperaments.

Maternal depression may influence feeding practices important in determining child eating behaviors and weight. However, the association between maternal depressive symptoms and feeding practices has been inconsistent, and most prior studies used self-report questionnaires alone to characterize feeding. The purpose of this study was to identify feeding practices associated with maternal depressive symptoms using multiple methodologies, and to test the hypothesis that maternal depressive symptoms are associated with less responsive feeding practices.