576Is the method of longitudinal data analysis equally relevant for common versus uncommon endpoints?

Background We explored the effects of predominant breastfeeding on infection-related hospitalization (uncommon outcome), over the first year of life, using the Mother Infant Health cohort study (MIHS), and the effect of early antiretroviral treatment (ART) on viral suppression (< 400 copies/mL) (common outcome), in children aged 7 to 12 weeks, using a subset of the Children with HIV Early AntiRetroviral Treatment (CHER) clinical trial data. We assessed the sensitivity of findings to different models to account for dependency of uncommon and common binary outcome. Methods We fitted generalized linear mixed model with (1) random intercept and (2) random slope, generalized estimating equations (GEE) with 3) an exchangeable correlation structure; 4) autoregressive correlation structure of order 1 (AR1) and 5) unstructured correlation structure and 6) logistic regression model. Results Eighty four and 119 children from MIHS were non-predominantly and predominantly breastfed, respectively. There were 34 infection-related hospitalizations overall. Most infants were hospitalized once, except for four with two hospitalizations. We analysed 88 HIV-infected children from the CHER trial. On average, a child achieved viral suppression twice, range of one to four. The effect of predominant breastfeeding on infection-related hospitalization was similar across all models, except for the GEE with AR1 that had a high estimate (wider confidence intervals). The effect of early ART exposure on viral suppression varied across models. Conclusions The sensitivity of estimates to the method of analysis was driven by frequency of the outcome.

Changes in Core Competencies among Korean University Students Due to Remote Learning during the COVID-19 Pandemic

This study aimed to determine the academic performance and learning skills of students who studied through remote teaching methods during the coronavirus disease 2019 (COVID-19) pandemic. It was conducted in February 2021 with 398 university students in South Korea. Data were collected through online surveys. Generalized estimating equations (GEEs) with an autoregressive correlation structure were employed to distinguish differences in core competencies, academic performance, satisfaction, and usefulness of teaching methods before 2019 and after the COVID-19 pandemic. The findings revealed that the overall core competencies of participants were significantly lower in 2020 than before the COVID-19 pandemic. Furthermore, knowledge construction, responsibility practice, and socialization were significantly low during the COVID-19 pandemic, whereas information management and identity value did not show a significant difference. However, problem-solving was higher during the COVID-19 pandemic. Enhancing the core competencies of university students is integral in the new learning environment of the post-COVID-19 era. It is necessary to devise approaches that improve the effectiveness of remote teaching methods and simultaneously augment student satisfaction.

Growth Trajectories in Genetic Subtypes of Prader–Willi Syndrome

Prader–Willi syndrome (PWS) is a rare disorder caused by the loss of expression of genes on the paternal copy of chromosome 15q11-13. The main molecular subtypes of PWS are the deletion of 15q11-13 and non-deletion, and differences in neurobehavioral phenotype are recognized between the subtypes. This study aimed to investigate growth trajectories in PWS and associations between PWS subtype (deletion vs. non-deletion) and height, weight and body mass index (BMI). Growth data were available for 125 individuals with PWS (63 males, 62 females), of which 72 (57.6%) had the deletion subtype. There was a median of 28 observations per individual (range 2–85), producing 3565 data points distributed from birth to 18 years of age. Linear mixed models with cubic splines, subject-specific random effects and an autoregressive correlation structure were used to model the longitudinal growth data whilst accounting for the nature of repeated measures. Height was similar for males in both PWS subtypes, with non-deletion females being shorter than deletion females for older ages. Weight and BMI were estimated to be higher in the deletion subtype compared to the non-deletion subtype, with the size of difference increasing with advancing age for weight. These results suggest that individuals with deletion PWS are more prone to obesity.

Adherence of Umm Al-Qura University Dental Students to Infection Control Guidelines: A Four Year – Auditing Report

BACKGROUND: Infection control auditing is an objective quality improvement process that evaluates current practice against already available standards and guidelines. AIM: The aim of the study was to assess the adherence of Umm Al-Qura University dental students to infection control guidelines by 4 years’ clinical auditing. MATERIALS AND METHODS: A cross-sectional observational study of audit checklists (n = 40725) at Dental Teaching Hospital, Umm Al-Qura University, throughout 4 academic years (2015–2018) was performed. Checklists item, total category, and overall adherence percentages were calculated based on recorded observations. The difference in adherence and violations was assessed using generalized estimating equations with the identity logit and an autoregressive correlation matrix. RESULTS: Overall adherence to all checklist categories was high except for 10–45% got out of the cubicle with used gloves and 15–60% not probably wore mask outside the cubicle. Overall violations among females were highly statistically significant lower than males (OR: 0.926, p < 0.01) and 4th grade were statistically significant lower than among 6th grade (OR: 0.932, p < 0.05) while no statistically significant difference in overall violation among 5th grade in comparison to 6th grade. However, along the 4 years of the study, statistically significant difference in overall violations was observed. CONCLUSION: Adherence of Umm Al-Qura University dental students to infection control guidelines in the past 4 years remained consistently high except for attitude in the clinic station outside the cubicle which improved along study years. Our results highlight the importance of continuous monitoring through clinical audits together with educational programs and counseling with students violating infection control policies to make corrective actions.

Associations of the first occurrence of pathogen-specific clinical mastitis with milk yield and milk composition in dairy cows

The aim of this study was to estimate the associations of the first occurrence of pathogen-specific clinical mastitis (CM) with milk yield and milk composition (somatic cell count (SCC), lactose, fat, protein content in milk and milk urea nitrogen (MUN)). We studied 3149 dairy cows in 31 Hokkaido dairy farms in Japan. Five pathogen groups were studied: Streptococcus spp.; Staphylococcus aureus (S. aureus); coagulase-negative staphylococci (CNS); coliforms; and fungi. Test-day milk data and clinical records were collected from June 2011 until February 2014. Mixed models with an autoregressive correlation structure were fitted to quantify the effects of CM and several other control variables (herd, calving season, parity, week of lactation, and other diseases). Primipara (first lactation) and multipara (second and later lactations) were analysed separately. All pathogens, particularly S. aureus and fungi, were associated with significant milk losses in multipara. In this study, S. aureus and CNS infections were not associated with significant milk loss in primipara. All pathogens, in particular S. aureus and fungi, significantly increased SCC in both parity groups. All pathogens, especially CNS (in primipara) and S. aureus (in multipara), decreased lactose content. All pathogen groups except for fungi were associated with significant changes in fat, protein and MUN. Some pathogens such as Streptococcus spp. and coliforms seemed to be associated with long-term fat, protein and MUN changes. These findings provide estimates that could be used to calculate precise costs of CM, and also provide better indicators of pathogen-specific mastitis.

Variance modelling of longitudinal height data from a Pinus radiata progeny test

Variance components were estimated using alternative structures for the additive genetic covariance matrix (G0), for height (m) of trees measured at 10 unequally spaced ages in an open-pollinated progeny test. These structures reflected unstructured, autoregressive, banded correlation and random regressions models. The residual matrix (R0) was unstructured, and the block and plot strata matrices were autoregressive. The best model for G0 considering the likelihood value and number of parameters was the autoregressive correlation form with age-specific variances and time on a natural logarithm basis. The genetic correlation between successive measures ranged from 0.93 at age 1 to 0.99 at age 14 years. Heritability increased with age from 0.09 (age 1) to 0.24 (age 7) and then declined to 0.13 at age 15. Heritabilities from the unstructured model were similar, while heritabilities assuming banded correlations were lower after age 7. The covariance structure implicit in the random regressions model was considered unsatisfactory. Using structures in G0 facilitated model fitting and convergence of the likelihood maximisation algorithm. Fitting a structured matrix that reflects the relationships present in repeated measures may overcome problems of nonpositive definiteness of unstructured matrices from longitudinal data, especially when genetic variation is small.

Product autoregression: a time-series characterization of the gamma distribution

A non-linear stationary stochastic process {Xt} is derived and shown to have the property that both the processes {Xt} and {log Xt} have the same correlation structure, viz. the Markov or first-order autoregressive correlation structure. The generation of such processes is discussed briefly and a characterization of the gamma distribution is obtained.

Product autoregression: a time-series characterization of the gamma distribution

A non-linear stationary stochastic process {Xt } is derived and shown to have the property that both the processes {Xt } and {log Xt } have the same correlation structure, viz. the Markov or first-order autoregressive correlation structure. The generation of such processes is discussed briefly and a characterization of the gamma distribution is obtained.