Murthy N. Mittinty

A review on degradation models in reliability analysis

With increasingly complex engineering assets and tight economic requirements, asset reliability becomes more crucial in Engineering Asset Management (EAM). Improving the reliability of systems has always been a major aim of EAM. Reliability assessment using degradation data has become a significant approach to evaluate the reliability and safety of critical systems. Degradation data often provide more information than failure time data for assessing reliability and predicting the remnant life of systems. In general, degradation is the reduction in performance, reliability, and life span of assets. Many failure mechanisms can be traced to an underlying degradation process. Degradation phenomenon is a kind of stochastic process; therefore, it could be modelled in several approaches. Degradation modelling techniques have generated a great amount of research in reliability field. While degradation models play a significant role in reliability analysis, there are few review papers on that. This paper presents a review of the existing literature on commonly used degradation models in reliability analysis. The current research and developments in degradation models are reviewed and summarised in this paper. This study synthesises these models and classifies them in certain groups. Additionally, it attempts to identify the merits, limitations, and applications of each model. It provides potential applications of these degradation models in asset health and reliability prediction.

Jurisdictional, socioeconomic and gender inequalities in child health and development: analysis of a national census of 5-year-olds in Australia

Objectives Early child development may have important consequences for inequalities in health and well-being. This paper explores population level patterns of child development across Australian jurisdictions, considering socioeconomic and demographic characteristics. Design Census of child development across Australia. Setting and participants Teachers complete a developmental checklist, the Australian Early Development Index (AEDI), for all children in their first year of full-time schooling. Between May and July 2009, the AEDI was collected by 14 628 teachers in primary schools (government and non-government) across Australia, providing information on 261 147 children (approximately 97.5% of the estimated 5-year-old population). Outcome measures Level of developmental vulnerability in Australian children for five developmental domains: physical well-being, social competence, emotional maturity, language and cognitive skills and communication skills and general knowledge. Results The results show demographic and socioeconomic inequalities in child development as well as within and between jurisdiction inequalities. The magnitude of the overall level of inequality in child development and the impact of covariates varies considerably both between and within jurisdiction by sex. For example, the difference in overall developmental vulnerability between the best-performing and worst-performing jurisdiction is 12.5% for males and 7.1% for females. Levels of absolute social inequality within jurisdictions range from 8.2% for females to 12.7% for males. Conclusions The different mix of universal and targeted services provided within jurisdictions from pregnancy to age 5 may contribute to inequality across the country. These results illustrate the potential utility of a developmental census to shed light on the impact of differences in universal and targeted services to support child development by school entry.

Associations between dietary patterns at 6 and 15 months of age and sociodemographic factors

BACKGROUND/OBJECTIVES:Data from the Avon Longitudinal Study of Parents and Children (ALSPAC) have previously shown that dietary patterns are observable by 3 years. However, it is not clear when dietary patterns emerge. We aimed to describe dietary patterns in early life and their associations with maternal and infant sociodemographic characteristics.SUBJECTS/METHODS:Principal component analysis was applied to diet questionnaires of ALSPAC participants at 6 months (n=7052) and 15 months (n=5610) to extract dietary patterns. The sociodemographic factors associated with dietary patterns were investigated using regression analyses.RESULTS:Four dietary patterns were extracted at both 6 and 15 months. A traditional-style pattern characterized by home-prepared meats, vegetables and desserts, a second pattern characterized by ready-prepared baby foods and a third pattern characterized by discretionary foods such as biscuits, sweets and crisps were identified at both ages. At 6 months, the fourth pattern was characterized predominantly by breastfeeding and at 15 months, by contemporary-style foods including herbs, legumes, nuts, raw fruit and vegetables. Higher maternal age and education, number of siblings and lower body mass index (BMI) was associated with higher scores on the breastfeeding or meat, vegetables and desserts patterns, whereas higher discretionary food pattern scores were associated with younger maternal age, lower education, higher BMI and more siblings. Associations between sociodemographic factors and the ready-prepared baby food pattern scores were inconsistent across ages.CONCLUSIONS:Dietary patterns emerge from infancy and are associated with sociodemographic characteristics.

A review on reliability models with covariates

Modern Engineering Asset Management (EAM) requires the accurate assessment of current and the prediction of future asset health condition. Suitable mathematical models that are capable of predicting Time-to-Failure (TTF) and the probability of failure in future time are essential. In traditional reliability models, the lifetime of assets is estimated using failure time data. However, in most real-life situations and industry applications, the lifetime of assets is influenced by different risk factors, which are called covariates. The fundamental notion in reliability theory is the failure time of a system and its covariates. These covariates change stochastically and may influence and/or indicate the failure time. Research shows that many statistical models have been developed to estimate the hazard of assets or individuals with covariates. An extensive amount of literature on hazard models with covariates (also termed covariate models), including theory and practical applications, has emerged. This paper is a state-of-the-art review of the existing literature on these covariate models in both the reliability and biomedical fields. One of the major purposes of this expository paper is to synthesise these models from both industrial reliability and biomedical fields and then contextually group them into non-parametric and semiparametric models. Comments on their merits and limitations are also presented. Another main purpose of this paper is to comprehensively review and summarise the current research on the development of the covariate models so as to facilitate the application of more covariate modelling techniques into prognostics and asset health management.

Do Dietary Trajectories between Infancy and Toddlerhood Influence IQ in Childhood and Adolescence? Results from a Prospective Birth Cohort Study

Objective We examined whether trajectories of dietary patterns from 6 to 24 months of age are associated with intelligence quotient (IQ) in childhood and adolescence. Methods Participants were children enrolled in a prospective UK birth cohort (n = 7652) who had IQ measured at age 8 and/or 15 years. Dietary patterns were previously extracted from questionnaires when children were aged 6, 15 and 24 months using principal component analysis. Dietary trajectories were generated by combining scores on similar dietary patterns across each age, using multilevel mixed models. Associations between dietary trajectories and IQ were examined in generalized linear models with adjustment for potential confounders. Results Four dietary pattern trajectories were constructed from 6 to 24 months of age and were named according to foods that made the strongest contribution to trajectory scores; Healthy (characterised by breastfeeding at 6 months, raw fruit and vegetables, cheese and herbs at 15 and 24 months); Discretionary (biscuits, chocolate, crisps at all ages), Traditional (meat, cooked vegetables and puddings at all ages) and, Ready-to-eat (use of ready-prepared baby foods at 6 and 15 months, biscuits, bread and breakfast cereals at 24 months). In fully-adjusted models, a 1 SD change in the Healthy trajectory was weakly associated with higher IQ at age 8 (1.07 (95%CI 0.17, 1.97)) but not 15 years (0.49 (−0.28, 1.26)). Associations between the Discretionary and Traditional trajectories with IQ at 8 and 15 years were as follows; Discretionary; 8 years −0.35(−1.03, 0.33), 15 years −0.73(−1.33, −0.14) Traditional; 8 years −0.19(−0.71, 0.33)15 years −0.41(−0.77, −0.04)). The Ready-to-eat trajectory had no association with IQ at either age (8 years 0.32(−4.31, 4.95), 15 years 1.11(−3.10, 5.33). Conclusions The Discretionary and Traditional dietary pattern trajectories from 6 to 24 months of age, over the period when food patterns begin to emerge, are weakly associated with IQ in adolescence.

Diet spanning infancy and toddlerhood is associated with child blood pressure at age 7.5 y

BACKGROUND Diet in the first 2 y of life may be a pivotal period regarding effects on future blood pressure (BP). However, data on early-life diet and BP in childhood are sparse. OBJECTIVE We prospectively assessed associations between types of diet spanning infancy and toddlerhood (ie, transition diets across the complementary feeding period) and BP at age 7.5 y. DESIGN In a birth cohort study (Avon Longitudinal Study of Parents and Children; United Kingdom), a total of 1229 children had complete dietary intake data at 6, 15, and 24 mo; BP data at 7.5 y of age; and all 18 covariables. RESULTS Of the 2 transition diets that were extracted by using principal components analysis, the less-healthy diet was associated with an increase in systolic BP of 0.62 mm Hg (95% CI: 0.00, 1.24 mm Hg) and an increase in diastolic BP of 0.55 mm Hg (95% CI: 0.10, 1.00 mm Hg) for every one-unit (SD) increase in the less-healthy-diet score after adjustment for 15 potential confounders, including maternal characteristics and sociodemographic factors, birth variables, and breastfeeding duration. In contrast with systolic BP, the positive association between the less-healthy transition-diet score and diastolic BP persisted after additional adjustment for child body-size factors [height, body mass index (BMI), and waist circumference] at 7.5 y. CONCLUSIONS A less-healthy transition diet by age 2 y was associated with higher BP at 7.5 y. The BMI-related reduction in effect size reinforces the importance of BMI on the diet-BP relation.

Efficacy of infant simulator programmes to prevent teenage pregnancy: a school-based cluster randomised controlled trial in Western Australia.

BACKGROUND Infant simulator-based programmes, which aim to prevent teenage pregnancy, are used in high-income as well as low-income and middle-income countries but, despite growing popularity, no published evidence exists of their long-term effect. The aim of this trial was to investigate the effect of such a programme, the Virtual Infant Parenting (VIP) programme, on pregnancy outcomes of birth and induced abortion in Australia. METHODS In this school-based pragmatic cluster randomised controlled trial, eligible schools in Perth, Western Australia, were enrolled and randomised 1:1 to the intervention and control groups. Randomisation using a table of random numbers without blocking, stratification, or matching was done by a researcher who was masked to the identity of the schools. Between 2003 and 2006, the VIP programme was administered to girls aged 13-15 years in the intervention schools, while girls of the same age in the control schools received the standard health education curriculum. Participants were followed until they reached 20 years of age via data linkage to hospital medical and abortion clinic records. The primary endpoint was the occurrence of pregnancy during the teenage years. Binomial and Cox proportional hazards regression was used to test for differences in pregnancy rates between study groups. This study is registered as an international randomised controlled trial, number ISRCTN24952438. FINDINGS 57 (86%) of 66 eligible schools were enrolled into the trial and randomly assigned 1:1 to the intervention (28 schools) or the control group (29 schools). Then, between Feb 1, 2003, and May 31, 2006, 1267 girls in the intervention schools received the VIP programme while 1567 girls in the control schools received the standard health education curriculum. Compared with girls in the control group, a higher proportion of girls in the intervention group recorded at least one birth (97 [8%] of 1267 in the intervention group vs 67 [4%] of 1567 in the control group) or at least one abortion as the first pregnancy event (113 [9%] vs 101 [6%]). After adjustment for potential confounders, the intervention group had a higher overall pregnancy risk than the control group (relative risk 1·36 [95% CI 1·10-1·67], p=0·003). Similar results were obtained with the use of proportional hazard models (hazard ratio 1·35 [95% CI 1·10-1·67], p=0·016). INTERPRETATION The infant simulator-based VIP programme did not achieve its aim of reducing teenage pregnancy. Girls in the intervention group were more likely to experience a birth or an induced abortion than those in the control group before they reached 20 years of age. FUNDING Western Australian Health Promotion Foundation (Healthway), Lotteries WA, the Western Australian Department of Education and Training, and the Western Australian Department of Health.

Child care quality and children's cognitive and socio-emotional development: an Australian longitudinal study

There is growing evidence that high-quality non-parental child care can contribute to childrens learning, development and successful transition to school. Research examining the quality of child care and the effect on childrens development is not well documented outside the USA. We used data from the Longitudinal Study of Australian Children to examine the association between domain-specific aspects of child care quality at ages two to three and childrens cognitive (receptive vocabulary, literacy, maths proficiency) and socio-emotional development (internalising, externalising behaviours) at ages four to five and six to seven (n = 772–1136, depending on outcome). After extensive controls for parent, family and child background characteristics, higher quality relationships were associated with higher receptive vocabulary, literacy and maths scores and lower internalising and externalising problem behaviour scores at four to five and these effects although weaker, were still evident at ages six to seven. Activities in child care and provider/programme characteristics of care were not associated with childrens developmental outcomes.

Changes in Socioeconomic Inequality in Indonesian Children’s Cognitive Function from 2000 to 2007: A Decomposition Analysis

Background Measuring social inequalities in health is common; however, research examining inequalities in child cognitive function is more limited. We investigated household expenditure-related inequality in children’s cognitive function in Indonesia in 2000 and 2007, the contributors to inequality in both time periods, and changes in the contributors to cognitive function inequalities between the periods. Methods Data from the 2000 and 2007 round of the Indonesian Family Life Survey (IFLS) were used. Study participants were children aged 7–14 years (n = 6179 and n = 6680 in 2000 and 2007, respectively). The relative concentration index (RCI) was used to measure the magnitude of inequality. Contribution of various contributors to inequality was estimated by decomposing the concentration index in 2000 and 2007. Oaxaca-type decomposition was used to estimate changes in contributors to inequality between 2000 and 2007. Results Expenditure inequality decreased by 45% from an RCI = 0.29 (95% CI 0.22 to 0.36) in 2000 to 0.16 (95% CI 0.13 to 0.20) in 2007 but the burden of poorer cognitive function was higher among the disadvantaged in both years. The largest contributors to inequality in child cognitive function were inequalities in per capita expenditure, use of improved sanitation and maternal high school attendance. Changes in maternal high school participation (27%), use of improved sanitation (25%) and per capita expenditures (18%) were largely responsible for the decreasing inequality in children’s cognitive function between 2000 and 2007. Conclusions Government policy to increase basic education coverage for women along with economic growth may have influenced gains in children’s cognitive function and reductions in inequalities in Indonesia.

Impact of Prolonged Breastfeeding on Dental Caries: A Population-Based Birth Cohort Study

Rigorous methodology and sophisticated statistical analysis improve the evidence of prolonged breastfeeding as a risk factor for primary dental caries. BACKGROUND: Few studies have assessed the effect of breastfeeding, bottle feeding, and sugar consumption on children’s dental caries. We investigated whether the duration of breastfeeding is a risk factor for dental caries in the primary dentition, independently of sugar consumption. METHODS: An oral health study (n = 1303) nested in a birth cohort study was carried out in southern Brazil. The average number of decayed, missing, and filled primary tooth surfaces (dmfs) and severe early childhood caries (S-ECC: dmfs ≥6) were investigated at age 5 years. Breastfeeding was the main exposure collected at birth and at 3, 12, and 24 months of age. Data on sugar consumption were collected at 24, 48, and 60 months of age. Marginal structural modeling was used to estimate the controlled direct effect of breastfeeding (0–12, 13–23, and ≥24 months) on dmfs and on S-ECC. RESULTS: The prevalence of S-ECC was 23.9%. The mean number of dmfs was 4.05. Children who were breastfed for ≥24 months had a higher number of dmfs (mean ratio: 1.9; 95% confidence interval: 1.5–2.4) and a 2.4 times higher risk of having S-ECC (risk ratio: 2.4; 95% confidence interval: 1.7–3.3) than those who were breastfed up to 12 months of age. Breastfeeding between 13 and 23 months had no effect on dental caries. CONCLUSIONS: Prolonged breastfeeding increases the risk of having dental caries. Preventive interventions for dental caries should be established as early as possible because breastfeeding is beneficial for children’s health. Mechanisms underlying this process should be investigated more deeply.