Biomedical subjects

Michael L Pennell

Publications and source records attributed to Michael L Pennell.

3 recordsLinked to original sources

PubMed2006

Bayesian semiparametric dynamic frailty models for multiple event time data.

Many biomedical studies collect data on times of occurrence for a health event that can occur repeatedly, such as infection, hospitalization, recurrence of disease, or tumor onset. To analyze such data, it is necessary to account for within-subject dependency in the multiple event times. Motivated by data from studies of palpable tumors, this article proposes a dynamic frailty model and Bayesian semiparametric approach to inference. The widely used shared frailty proportional hazards model is generalized to allow subject-specific frailties to change dynamically with age while also accommodating nonproportional hazards. Parametric assumptions on the frailty distribution are avoided by using Dirichlet process priors for a shared frailty and for multiplicative innovations on this frailty. By centering the semiparametric model on a conditionally conjugate dynamic gamma model, we facilitate posterior computation and lack-of-fit assessments of the parametric model. Our proposed method is demonstrated using data from a cancer chemoprevention study.

Algorithms↗

PubMed2005

Maternal smoking during pregnancy in relation to child overweight: follow-up to age 8 years.

BACKGROUND: Data from several studies indicate that children of mothers who smoked during pregnancy may be at a risk of overweight compared with children of non-smoking mothers. The size of this relation, however, is unclear, as is the age at which it becomes detectable. METHODS: Prospective data for 34 866 children enrolled in the US Collaborative Perinatal Project were analysed to examine maternal pregnancy smoking in relation to weight, height, and body mass index (BMI) in offspring at ages 1, 3, 4, 7, and 8 years. RESULTS: Compared with offspring of non-smokers, children of smokers had (i) weight that was lower at birth but then quickly equalled or exceeded that of non-smokers, (ii) consistently decreased height, and (iii) increased risk of overweight, particularly in girls. For example, at age 7 years, the adjusted odds ratio of BMI>or=85th percentile in boys of mothers who smoked on an average>or=20 cigarettes per day while pregnant was 1.22 (95% confidence interval 1.03-1.46), and in girls it was 1.30 (1.08-1.56). CONCLUSIONS: In these data, maternal smoking during pregnancy was associated with a modest increase in risk of overweight in children before the age of 8 years.

Birth Weight↗

PubMed2005

Energy costs of physical activities in children and adolescents.

PURPOSE: The primary aim was to determine the energy expenditure (EE: kcal.kg(-1).h(-1)) in terms of caloric cost and metabolic equivalents of activities commonly performed by children and adolescents. Secondary aims were to determine at what age and pubertal developmental stage values approach those of adults. METHODS: In this descriptive study, 295 volunteer youth 8-18 yr of age completed 18 common physical activities (including rest) while EE was measured continuously with a portable metabolic system. Three sets of activities were assigned in random order for each subject. Activities ranged from television viewing and video game play to running and rope skipping. Pubertal development was estimated from a self-report questionnaire. RESULTS: At rest, VO(2) and EE were highest in the youngest children and decreased with advancing age and higher pubertal stage in both genders. The age-adjusted and puberty-adjusted energy expenditure values were generally lower than the compendium MET values for sedentary and moderate activities but were more varied for high-intensity activities. However, the ratio of activity EE to REE was comparable in children and adults. CONCLUSIONS: Energy expenditure per kilogram of body mass at rest or during exercise is greater in children than adults and varies with pubertal status, thus using the definition of a MET in the compendium of physical activities without adjustment is inadequate for energy estimation in children, until a child reaches Tanner Stage 5. However, the ratio of activity EE to resting EE in children appears to be similar or slightly less than in the compendium, suggesting that the compendium MET increments used with our adjusted EE values more closely approximate the true EE of activities in children than present adult norms.

Adolescent↗