9 resultados para longitudinal mediation models

em QUB Research Portal - Research Directory and Institutional Repository for Queen's University Belfast


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Background
Learning to read is a key goal during primary school: reading difficulties may curtail children’s learning trajectories. Controversy remains regarding what types of interventions are effective for children at risk for academic failure, such as children in disadvantaged areas. We present data from a complex intervention to test the hypothesis that phonic skills and word recognition abilities are a pivotal and specific causal mechanism for the development of reading skills in children at risk for poorer literacy outcomes.
Method
Over 500 pupils across 16 primary schools took part in a Cluster Randomised Controlled Trial from school year 1 to year 3. Schools were randomly allocated to the intervention or the control arm. The intervention involved a literacy-rich after-school programme. Children attending schools in the control arm of the study received the curriculum normally provided. Children in both arms completed batteries of language, phonic skills, and reading tests every year. We used multilevel mediation models to investigate mediating processes between intervention and outcomes.
Findings
Children who took part in the intervention displayed improvements in reading skills compared to those in the control arm. Results indicated a significant indirect effect of the intervention via phonics encoding.
Discussion
The results suggest that the intervention was effective in improving reading abilities of children at risk, and this effect was mediated by improving children’s phonic skills. This has relevance for designing interventions aimed at improving literacy skills of children exposed to socio-economic disadvantage. Results also highlight the importance of methods to investigate causal pathways from intervention to outcomes.

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Hypertension is a key risk factor for stroke, cardiovascular disease and dementia. Although the link between weight, sodium and hypertension is established in younger people, little is known about their inter-relationship in people beyond 80 years of age. Associations between blood pressure, anthropometric indices and sodium were investigated in 495 apparently healthy, community-living participants (age 90, SD 4.8; range 80–106), from the cross-sectional Belfast Elderly Longitudinal Free-living Aging STudy (BELFAST) study. In age-sex-adjusted logistic regression models, blood pressure =140/90 mmHg significantly associated with body mass index (BMI) [odds ratio (OR)?=?1.28/ kg/m2], with weight (OR?=?1.22/kg) approaching significance (P?=?0.07). In further age-sex-adjusted models, blood pressure above the 120/80 mmHg normotensive reference value significantly associated with BMI (OR?=?1.44/kg/m2), weight (OR?=?1.36/kg), skin-fold-thickness (OR?=?1.33/mm) and serum sodium (OR?=?1.37 mmol/l). In BELFAST participants over 80 years old, blood pressure =140/90 mmHg is associated with BMI, in apparently similar ways to younger groups.

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BACKGROUND:

Many studies have suggested that caregiving has a detrimental impact on health. However, these conclusions are challenged by research which finds evidence of a comparative survivorship advantage, as well as work which controls for group differences in the demand for care.

METHODS:

We use a large record linkage study of England and Wales to investigate the mortality risks of carers identified in the 2001 Census. The analysis focuses on individuals aged 35-74 living with others in private households and a distinction is made between those providing 1-19 and 20 or more hours of care per week. Logit models identify differences in carers' health at baseline and postcensal survival is analysed using Cox proportional hazards models.

RESULTS:

12.2% of study members reported providing 1-19 h of care and 5.4% reported providing 20 or more hours. While carers were significantly more likely to report poorer health at baseline, survival analyses suggested that they were at a significantly lower risk of dying. This comparative advantage also held when the analyses were restricted to individuals living with at least one person with poor health.

CONCLUSIONS:

The comparative mortality advantage revealed in this analysis challenges common characterisations of carers' health and draws attention to important differences in the way carers are defined in existing analyses. The survival results are consistent with work using similar data for Northern Ireland. However, the study also affords more uniform conclusions about carers' baseline health and this provides grounds for questioning existing hypotheses about the reasons for this advantage.

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Background: Durkheim’s seminal historical study demonstrated that religious affiliation reduces suicide risk, but it is unclear whether this protective effect persists in modern, more secular societies.

Aims: To examine suicide risk according to Christian religious affiliation and by inference to examine underlying mechanisms for suicide risk. If church attendance is important, risk should be lowest for Roman Catholics and highest for those with no religion; if religiosity is important, then ‘conservative’ Christians should fare best.

Method: A 9-year study followed 1 106 104 people aged 16–74 years at the 2001 UK census, using Cox proportional hazards models adjusted for census-based cohort attributes.

Results: In fully adjusted models analysing 1119 cases of suicide, Roman Catholics, Protestants and those professing no religion recorded similar risks. The risk associated with conservative Christians was lower than that for Catholics (HR = 0.71, 95% CI 0.52–0.97).

Conclusions: The relationship between religious affiliation and suicide established by Durkheim may not pertain in societies where suicide rates are highest at younger ages. Risks are similar for those with and without a religious affiliation, and Catholics (who traditionally are characterised by higher levels of church attendance) do not demonstrate lower risk of suicide. However, religious affiliation is a poor measure of religiosity, except for a small group of conservative Christians, although their lower risk of suicide may be attributable to factors such as lower risk behaviour and alcohol consumption.

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Background There has been an increasing interest in the health effects of long
working hours, but little empirical evidence to substantiate early
10 case series suggesting an increased mortality risk. The aim of the
current study is to quantify the mortality risk associated with long
working hours and to see if this varies by employment relations and
conditions of occupation.
Methods A census-based longitudinal study of 414 949 people aged 20-59/64
15 years, working at least 35 h/week, subdivided into four occupational
classes (managerial/professional, intermediate, own account workers,
workers in routine occupations) with linkage to deaths records
over the following 8.7 years. Cox proportional hazards models were
used to examine all-cause and cause-specific mortality risk.
20 Results Overall 9.4% of the cohort worked 55 or more h/week, but this
proportion was greater in the senior management and professional
occupations and in those who were self-employed. Analysis of 4447
male and 1143 female deaths showed that hours worked were
associated with an increased risk of all-cause mortality only for
25 men working for more than 55 or more h/week in routine/semiroutine
occupations [adjusted hazard ratios (adjHR) 1.31: 95%
confidence intervals (CIs) 1.11, 1.55)] compared with their peers
working 35–40 h/week. Their equivalent risk of death from cardiovascular
disease was (adjHR 1.49: 95% CIs 1.10, 2.00).
30 Conclusions These findings substantiate and add to the earlier studies indicating
the deleterious impact of long working hours but also suggest that
the effects are moderated by employment relations or conditions of
occupation. The policy implications of these findings are discussed.

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The current worldwide nursing shortage and high attrition of nursing students remain a challenge for the nursing profession. The aim of this paper was to investigate how key psychological attributes and constructions differentiate between completers and non-completers of nursing education. A questionnaire including measures of gender role identity and perceived gender appropriateness of careers was administered to 384 students early in the first year of the course. At the end of the programme attrition rates were obtained. The findings indicate that males were more likely to leave the course than females. Furthermore, those who completed the course tended to view nursing as more appropriate for women, in contrast to the non-completers who had less gender typed views. The female-dominated nature of nursing, prevalent stereotypes and gender bias inherent in nursing education seem to make this an uncomfortable place for males and those with less gendered typed views. Whilst it is acknowledged that attrition is undoubtedly a complex issue with many contributing factors, the nursing profession need to take steps to address this bias to ensure their profession is open equally to both female and male recruits.

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Robust joint modelling is an emerging field of research. Through the advancements in electronic patient healthcare records, the popularly of joint modelling approaches has grown rapidly in recent years providing simultaneous analysis of longitudinal and survival data. This research advances previous work through the development of a novel robust joint modelling methodology for one of the most common types of standard joint models, that which links a linear mixed model with a Cox proportional hazards model. Through t-distributional assumptions, longitudinal outliers are accommodated with their detrimental impact being down weighed and thus providing more efficient and reliable estimates. The robust joint modelling technique and its major benefits are showcased through the analysis of Northern Irish end stage renal disease patients. With an ageing population and growing prevalence of chronic kidney disease within the United Kingdom, there is a pressing demand to investigate the detrimental relationship between the changing haemoglobin levels of haemodialysis patients and their survival. As outliers within the NI renal data were found to have significantly worse survival, identification of outlying individuals through robust joint modelling may aid nephrologists to improve patient's survival. A simulation study was also undertaken to explore the difference between robust and standard joint models in the presence of increasing proportions and extremity of longitudinal outliers. More efficient and reliable estimates were obtained by robust joint models with increasing contrast between the robust and standard joint models when a greater proportion of more extreme outliers are present. Through illustration of the gains in efficiency and reliability of parameters when outliers exist, the potential of robust joint modelling is evident. The research presented in this thesis highlights the benefits and stresses the need to utilise a more robust approach to joint modelling in the presence of longitudinal outliers.