Michail Papathomas

Bayesian profile regression with an application to the National survey of children's health

Standard regression analyses are often plagued with problems encountered when one tries to make inference going beyond main effects using data sets that contain dozens of variables that are potentially correlated. This situation arises, for example, in epidemiology where surveys or study questionnaires consisting of a large number of questions yield a potentially unwieldy set of interrelated data from which teasing out the effect of multiple covariates is difficult. We propose a method that addresses these problems for categorical covariates by using, as its basic unit of inference, a profile formed from a sequence of covariate values. These covariate profiles are clustered into groups and associated via a regression model to a relevant outcome. The Bayesian clustering aspect of the proposed modeling framework has a number of advantages over traditional clustering approaches in that it allows the number of groups to vary, uncovers subgroups and examines their association with an outcome of interest, and fits the model as a unit, allowing an individuals outcome potentially to influence cluster membership. The method is demonstrated with an analysis of survey data obtained from the National Survey of Childrens Health. The approach has been implemented using the standard Bayesian modeling software, WinBUGS, with code provided in the supplementary material available at Biostatistics online. Further, interpretation of partitions of the data is helped by a number of postprocessing tools that we have developed.

Examining the joint effect of multiple risk factors using exposure risk profiles: lung cancer in nonsmokers.

Background Profile regression is a Bayesian statistical approach designed for investigating the joint effect of multiple risk factors. It reduces dimensionality by using as its main unit of inference the exposure profiles of the subjects that is, the sequence of covariate values that correspond to each subject. Objectives We applied profile regression to a case–control study of lung cancer in nonsmokers, nested within the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort, to estimate the combined effect of environmental carcinogens and to explore possible gene–environment interactions. Methods We tailored and extended the profile regression approach to the analysis of case–control studies, allowing for the analysis of ordinal data and the computation of posterior odds ratios. We compared and contrasted our results with those obtained using standard logistic regression and classification tree methods, including multifactor dimensionality reduction. Results Profile regression strengthened previous observations in other study populations on the role of air pollutants, particularly particulate matter ≤ 10 μm in aerodynamic diameter (PM10), in lung cancer for nonsmokers. Covariates including living on a main road, exposure to PM10 and nitrogen dioxide, and carrying out manual work characterized high-risk subject profiles. Such combinations of risk factors were consistent with a priori expectations. In contrast, other methods gave less interpretable results. Conclusions We conclude that profile regression is a powerful tool for identifying risk profiles that express the joint effect of etiologically relevant variables in multifactorial diseases.

Exploring data from genetic association studies using Bayesian variable selection and the Dirichlet process: application to searching for gene × gene patterns.

We construct data exploration tools for recognizing important covariate patterns associated with a phenotype, with particular focus on searching for association with gene‐gene patterns. To this end, we propose a new variable selection procedure that employs latent selection weights and compare it to an alternative formulation. The selection procedures are implemented in tandem with a Dirichlet process mixture model for the flexible clustering of genetic and epidemiological profiles. We illustrate our approach with the aid of simulated data and the analysis of a real data set from a genome‐wide association study.

Blood Pressure Differences Associated With Optimal Macronutrient Intake Trial for Heart Health (OMNIHEART)–Like Diet Compared With a Typical American DietNovelty and Significance

The Dietary Approaches to Stop Hypertension-Sodium (DASH-Sodium) trial demonstrated beneficial effects on blood pressure (BP) of the DASH diet with lower sodium intake when compared with typical American diet. The subsequent Optimal Macronutrient Intake Trial for Heart Health (OMNIHEART) trial reported additional BP benefits from replacing carbohydrate in the DASH diet with either protein or monounsaturated fats. The primary aim of this study is to assess possible BP benefits of an OMNIHEART-like diet in free-living Americans using cross-sectional US population data of the International Study of Macronutrients, Micronutrients and Blood Pressure (INTERMAP) study. The INTERMAP data include four 24-hour dietary recalls, 2 timed 24-hour urine collections, 8 BP readings for 2195 individuals aged 40 to 59 years from 8 US INTERMAP population samples. Analyses are conducted using 2 approaches: (1) regression of BP on a linear OMNIHEART nutrient score calculated for each individual and (2) a Bayesian approach comparing estimated BP levels of an OMNIHEART-like nutrient profile with a typical American nutrient profile. After adjustment for potential confounders, an OMNIHEART score higher by 1 point was associated with systolic/diastolic BP differences of −1.0/−0.5 mm Hg (both P<0.001). Mean systolic/diastolic BPs were 111.3/68.4 and 115.2/70.6 mm Hg for Bayesian OMNIHEART and Control profiles, respectively, after controlling for possible confounders, with BP differences of −3.9/−2.2 mm Hg, P(difference ⩽0)=0.98/0.96. Findings were comparable for men and women, for nonhypertensive participants, and with adjustment for antihypertensive treatment. Our findings from data on US population samples indicate broad generalizability of OMNIHEART results beyond the trial setting and support recommendations for an OMNIHEART-style diet for prevention/control of population-wide adverse BP levels.The DASH-Sodium trial demonstrated beneficial effects on blood pressure (BP) of the DASH diet with lower sodium intake compared to typical American diet. The subsequent OMNIHEART trial reported additional BP benefits from replacing carbohydrate in the DASH diet with either protein or monounsaturated fats. The primary aim of this study is to assess possible BP benefits of an OMNIHEART-like diet in free-living Americans using cross-sectional U.S. population data of the INTERMAP Study. INTERMAP data include four 24-h dietary recalls, two timed 24-h urine collections, eight BP readings for 2,195 individuals ages 40-59 from eight US INTERMAP population samples. Analyses are conducted using two approaches: 1. Regression of BP on a linear OMNIHEART nutrient score calculated for each individual, and 2. A Bayesian approach comparing estimated BP levels of an OMNIHEART-like nutrient profile with a typical American nutrient profile. After adjustment for potential confounders, an OMNIHEART score higher by one point was associated with systolic/diastolic BP differences of −1.0/−0.5 mmHg (both P<0.001). Mean systolic/diastolic BPs were 111.3/68.4 and 115.2/70.6 mmHg for Bayesian OMNIHEART and Control profiles respectively, after controlling for possible confounders, with BP differences of −3.9/−2.2 mmHg, Pr(difference ≤ 0) ≈ 0.98/0.96. Findings were comparable for men and women, for non-hypertensive participants, and with adjustment for antihypertensive treatment. Our findings from data on US population samples indicate broad generalizability of OMNIHEART results beyond the trial setting, and support recommendations for an OMNIHEART-style diet for prevention/control of population-wide adverse BP levels.

Exploring dependence between categorical variables: Benefits and limitations of using variable selection within Bayesian clustering in relation to log-linear modelling with interaction terms

This manuscript is concerned with relating two approaches that can be used to explore complex dependence structures between categorical variables, namely Bayesian partitioning of the covariate space incorporating a variable selection procedure that highlights the covariates that drive the clustering, and log-linear modelling with interaction terms. We derive theoretical results on this relation and discuss if they can be employed to assist log-linear model determination, demonstrating advantages and limitations with simulated and real data sets. The main advantage concerns sparse contingency tables. Inferences from clustering can potentially reduce the number of covariates considered and, subsequently, the number of competing log-linear models, making the exploration of the model space feasible. Variable selection within clustering can inform on marginal independence in general, thus allowing for a more efficient exploration of the log-linear model space. However, we show that the clustering structure is not informative on the existence of interactions in a consistent manner. This work is of interest to those who utilize log-linear models, as well as practitioners such as epidemiologists that use clustering models to reduce the dimensionality in the data and to reveal interesting patterns on how covariates combine.

Blood pressure differences associated with Optimal Macronutrient Intake Trial for Heart Health (OMNIHEART)-like diet compared with a typical American diet

The Dietary Approaches to Stop Hypertension-Sodium (DASH-Sodium) trial demonstrated beneficial effects on blood pressure (BP) of the DASH diet with lower sodium intake when compared with typical American diet. The subsequent Optimal Macronutrient Intake Trial for Heart Health (OMNIHEART) trial reported additional BP benefits from replacing carbohydrate in the DASH diet with either protein or monounsaturated fats. The primary aim of this study is to assess possible BP benefits of an OMNIHEART-like diet in free-living Americans using cross-sectional US population data of the International Study of Macronutrients, Micronutrients and Blood Pressure (INTERMAP) study. The INTERMAP data include four 24-hour dietary recalls, 2 timed 24-hour urine collections, 8 BP readings for 2195 individuals aged 40 to 59 years from 8 US INTERMAP population samples. Analyses are conducted using 2 approaches: (1) regression of BP on a linear OMNIHEART nutrient score calculated for each individual and (2) a Bayesian approach comparing estimated BP levels of an OMNIHEART-like nutrient profile with a typical American nutrient profile. After adjustment for potential confounders, an OMNIHEART score higher by 1 point was associated with systolic/diastolic BP differences of −1.0/−0.5 mm Hg (both P<0.001). Mean systolic/diastolic BPs were 111.3/68.4 and 115.2/70.6 mm Hg for Bayesian OMNIHEART and Control profiles, respectively, after controlling for possible confounders, with BP differences of −3.9/−2.2 mm Hg, P(difference ⩽0)=0.98/0.96. Findings were comparable for men and women, for nonhypertensive participants, and with adjustment for antihypertensive treatment. Our findings from data on US population samples indicate broad generalizability of OMNIHEART results beyond the trial setting and support recommendations for an OMNIHEART-style diet for prevention/control of population-wide adverse BP levels.The DASH-Sodium trial demonstrated beneficial effects on blood pressure (BP) of the DASH diet with lower sodium intake compared to typical American diet. The subsequent OMNIHEART trial reported additional BP benefits from replacing carbohydrate in the DASH diet with either protein or monounsaturated fats. The primary aim of this study is to assess possible BP benefits of an OMNIHEART-like diet in free-living Americans using cross-sectional U.S. population data of the INTERMAP Study. INTERMAP data include four 24-h dietary recalls, two timed 24-h urine collections, eight BP readings for 2,195 individuals ages 40-59 from eight US INTERMAP population samples. Analyses are conducted using two approaches: 1. Regression of BP on a linear OMNIHEART nutrient score calculated for each individual, and 2. A Bayesian approach comparing estimated BP levels of an OMNIHEART-like nutrient profile with a typical American nutrient profile. After adjustment for potential confounders, an OMNIHEART score higher by one point was associated with systolic/diastolic BP differences of −1.0/−0.5 mmHg (both P<0.001). Mean systolic/diastolic BPs were 111.3/68.4 and 115.2/70.6 mmHg for Bayesian OMNIHEART and Control profiles respectively, after controlling for possible confounders, with BP differences of −3.9/−2.2 mmHg, Pr(difference ≤ 0) ≈ 0.98/0.96. Findings were comparable for men and women, for non-hypertensive participants, and with adjustment for antihypertensive treatment. Our findings from data on US population samples indicate broad generalizability of OMNIHEART results beyond the trial setting, and support recommendations for an OMNIHEART-style diet for prevention/control of population-wide adverse BP levels.

Blood Pressure Differences Associated with OMNIHEART-Like Diet Compared to a Typical American Diet

The Dietary Approaches to Stop Hypertension-Sodium (DASH-Sodium) trial demonstrated beneficial effects on blood pressure (BP) of the DASH diet with lower sodium intake when compared with typical American diet. The subsequent Optimal Macronutrient Intake Trial for Heart Health (OMNIHEART) trial reported additional BP benefits from replacing carbohydrate in the DASH diet with either protein or monounsaturated fats. The primary aim of this study is to assess possible BP benefits of an OMNIHEART-like diet in free-living Americans using cross-sectional US population data of the International Study of Macronutrients, Micronutrients and Blood Pressure (INTERMAP) study. The INTERMAP data include four 24-hour dietary recalls, 2 timed 24-hour urine collections, 8 BP readings for 2195 individuals aged 40 to 59 years from 8 US INTERMAP population samples. Analyses are conducted using 2 approaches: (1) regression of BP on a linear OMNIHEART nutrient score calculated for each individual and (2) a Bayesian approach comparing estimated BP levels of an OMNIHEART-like nutrient profile with a typical American nutrient profile. After adjustment for potential confounders, an OMNIHEART score higher by 1 point was associated with systolic/diastolic BP differences of −1.0/−0.5 mm Hg (both P<0.001). Mean systolic/diastolic BPs were 111.3/68.4 and 115.2/70.6 mm Hg for Bayesian OMNIHEART and Control profiles, respectively, after controlling for possible confounders, with BP differences of −3.9/−2.2 mm Hg, P(difference ⩽0)=0.98/0.96. Findings were comparable for men and women, for nonhypertensive participants, and with adjustment for antihypertensive treatment. Our findings from data on US population samples indicate broad generalizability of OMNIHEART results beyond the trial setting and support recommendations for an OMNIHEART-style diet for prevention/control of population-wide adverse BP levels.The DASH-Sodium trial demonstrated beneficial effects on blood pressure (BP) of the DASH diet with lower sodium intake compared to typical American diet. The subsequent OMNIHEART trial reported additional BP benefits from replacing carbohydrate in the DASH diet with either protein or monounsaturated fats. The primary aim of this study is to assess possible BP benefits of an OMNIHEART-like diet in free-living Americans using cross-sectional U.S. population data of the INTERMAP Study. INTERMAP data include four 24-h dietary recalls, two timed 24-h urine collections, eight BP readings for 2,195 individuals ages 40-59 from eight US INTERMAP population samples. Analyses are conducted using two approaches: 1. Regression of BP on a linear OMNIHEART nutrient score calculated for each individual, and 2. A Bayesian approach comparing estimated BP levels of an OMNIHEART-like nutrient profile with a typical American nutrient profile. After adjustment for potential confounders, an OMNIHEART score higher by one point was associated with systolic/diastolic BP differences of −1.0/−0.5 mmHg (both P<0.001). Mean systolic/diastolic BPs were 111.3/68.4 and 115.2/70.6 mmHg for Bayesian OMNIHEART and Control profiles respectively, after controlling for possible confounders, with BP differences of −3.9/−2.2 mmHg, Pr(difference ≤ 0) ≈ 0.98/0.96. Findings were comparable for men and women, for non-hypertensive participants, and with adjustment for antihypertensive treatment. Our findings from data on US population samples indicate broad generalizability of OMNIHEART results beyond the trial setting, and support recommendations for an OMNIHEART-style diet for prevention/control of population-wide adverse BP levels.

Primary education in Vietnam and pupil online engagement

This paper focuses on exploring the disparities in social awareness and use of the Internet between urban and rural school children in the North of Vietnam. Design/methodology/approach: A total of 525 pupils, aged 9 to 11 years old, randomly selected from 7 urban and rural schools, who are Internet users, participated in the study and consented to responding to a questionnaire adapted from an equivalent European Union (EU) study. A comparative statistical analysis of the responses was then carried out, using IBM SPSS v21, which consisted of a descriptive analysis, an identification of personal self-development opportunities, as well as issues related to pupils’ digital prowess and knowledge of Internet use, and Internet safety, including parental engagement in their offspring’s online activities. Findings: The study highlights the fact that children from both the urban and rural regions of the North of Vietnam mostly access to the Internet from home, but with more children in the urbanized areas accessing it at school than their rural counterparts. Although children from the rural areas scored lower on all the Internet indicators, such as digital access and online personal experience and awareness, there was no disparity in awareness of Internet risks between the two sub-samples. It is noteworthy that there was no statistically significant gender difference towards online activities that support self-development. In relation to safe Internet usage, children are likely to seek advice from their parents, rather than through teachers or friends. However, they are not yet provided with an effective safety net while exposing themselves to the digital world. Originality/value: Although the Vietnamese national curriculum on the Computer Science subject does not explicitly cover the use of the Internet and its related aspects, the majority of children who took part in this study claimed to have used the Internet in their learning activities. This emphasises the urgent need for the MoE and educators in the country to not only improve ICT facilities in schools, but also to revise the Computer Science curriculum in order to (a) provide a supportive environment for learning development and (b) collectively advocate the dynamics of Internet use in order to ensure safe access and use by the children.

418 BLOOD PRESSURE DIFFERENCES ASSOCIATED WITH DASH-LIKE LOWER SODIUM COMPARED WITH TYPICAL AMERICAN HIGHER SODIUM NUTRIENT PROFILE: INTERMAP USA

Background: The DASH-Sodium trial demonstrated beneficial effects on blood pressure (BP) of the DASH diet with lower sodium intake, compared to typical American diet with higher sodium. Objective: Assess possible BP benefits of a lower sodium DASH-like diet in free-living Americans using two statistical methods: a linear DASH nutrient score, and a Bayesian approach comparing estimated BP levels for a DASH-like lower sodium nutrient profile (“DASH-Na”) with those for a typical American higher sodium profile (“Control”). Design: Cross-sectional data include four 24-h dietary recalls, two timed 24-h urine collections, eight BP readings for 2,195 individuals ages 40–59 from eight US INTERMAP population samples. A DASH score (9 nutrient targets) was calculated for each participant and regressed on their BP. For Bayesian profile regression, participants were assigned to clusters based on similarity of their nutrient profiles. Pre-specified DASH-Na and Control profiles were also assigned to clusters. Posterior distributions were obtained for mean BP levels associated with DASH-Na and Control profiles. Results: One unit higher DASH score was associated with systolic/diastolic BP lower by 1.2/0.7 mmHg (both P < 0.001). Mean systolic/diastolic BPs were 114.6/71.4 and 122.6/75.4 mmHg for Bayesian DASH-Na and Control profiles respectively; controlled for possible confounders, average BP differences were −4.9/−2.1 mmHg (P = 0.01/0.08). Findings were comparable for men and women, for non-hypertensive participants, and with adjustment for antihypertensive treatment. Conclusions: Our findings from data on US population samples indicate broad generalisability of DASH-Sodium trial results, and support recommendations for a reduced sodium DASH-style diet for prevention/control of population-wide adverse BP levels.

Cardiologists' Awareness of the Impact of Air Pollution on Cardiovascular Disease in Vietnam and the Philippines -- Multiple Logistic Regression Modelling

The air pollution situation in Vietnam and the Philippines has deteriorated in recent years, and mortality rates from cardiovascular diseases (CVD) have remained in the top ten of all causes of deaths for the last few years. The aim of this paper is to understand and model the awareness of cardiologists of the potential impact of air pollution on CVD in both nations. A full-scale survey covering 321 cardiologists was conducted in Vietnam (27 hospitals across the country) and the Philippines (members of the Philippine Heart Association with a subset from Davao Province). The paper reports on extensive results obtained through logistic regression modelling.