This dissertation contains two empirical papers on income and premature mortality, and one methodological paper that concerns the summary measurement of the extent of social inequalities in health. Income dynamics and adult mortality: Canada and the USA Chapter 4 examines the effects of income level and income drops on all-cause mortality in Canada and the United States. The Canadian data are from the Longitudinal Administrative Databank (LAD), and the US data are from the Panel Study of Income Dynamics (PSID). The LAD consists of personal income tax records for 20% of Canadian filers from 1982 through 2005. The PSID is a survey sampled in 1968 and followed annually through 1997. Analyses of the PSID confirmed previously published findings that used alternative statistical methods. The effect of income level on hazard of death is twice as large in the United States. The effects of income drops differed in Canada and the United States. Income dynamics and adult mortality in Canada: Chapter 5 re-analyses the LAD data to refine causal inference regarding the effects of income level and income drops on all-cause mortality. Exposure at ages 40-55 is analyzed for induction times ranging from 1-18 years. Income level was defined as the mean of the previous five year period, and income drops was measured both as annual change, and as the difference between projected and observed income. The effect of income level attenuated very little over induction time, and was not confounded by work disability. The effect of income drops also attenuated very little over induction time. Men in couple families showed a monotonic dose-reponse effect of income drops, and exclusion of families with potentially confounding characteristics did not affect the estimated risks. The hypothesized dependency of the effect of income drops on income level was not observed. No differences were observed between the two measures of income drops. Overall, there is strong evidence that the effect of income level on risk of death is primarily causal, while evidence for the effect of income drops is mixed.

This dissertation contains two empirical papers on income and premature mortality, and one methodological paper that concerns the summary measurement of the extent of social inequalities in health. Income dynamics and adult mortality: Canada and the USA Chapter 4 examines the effects of income level and income drops on all-cause mortality in Canada and the United States. The Canadian data are from the Longitudinal Administrative Databank (LAD), and the US data are from the Panel Study of Income Dynamics (PSID). The LAD consists of personal income tax records for 20% of Canadian filers from 1982 through 2005. The PSID is a survey sampled in 1968 and followed annually through 1997. Analyses of the PSID confirmed previously published findings that used alternative statistical methods. The effect of income level on hazard of death is twice as large in the United States. The effects of income drops differed in Canada and the United States. Income dynamics and adult mortality in Canada: Chapter 5 re-analyses the LAD data to refine causal inference regarding the effects of income level and income drops on all-cause mortality. Exposure at ages 40-55 is analyzed for induction times ranging from 1-18 years. Income level was defined as the mean of the previous five year period, and income drops was measured both as annual change, and as the difference between projected and observed income. The effect of income level attenuated very little over induction time, and was not confounded by work disability. The effect of income drops also attenuated very little over induction time. Men in couple families showed a monotonic dose-reponse effect of income drops, and exclusion of families with potentially confounding characteristics did not affect the estimated risks. The hypothesized dependency of the effect of income drops on income level was not observed. No differences were observed between the two measures of income drops. Overall, there is strong evidence that the effect of income level on risk of death is primarily causal, while evidence for the effect of income drops is mixed.

Background: Serum estradiol levels decline after menopause and the effect on mental health-related quality of life (MHR-QOL) is unclear. Objective: To determine if there is an association between endogenous serum estradiol levels and MHR-QOL in healthy postmenopausal women. Methods: This cross-sectional study used baseline Canadian data from the Mammary Prevention.3 trial. Serum estradiol was measured with liquid chromatography-tandem mass spectrometry. Outcomes for MHR-QOL were the Medical Outcomes 36-Item Short Form Health Survey (SF-36) Mental Health Inventory-5 (MHI-5), Mental Component Summary (MCS), and the Menopause-Specific Quality of Life Questionnaire (MENQOL)-psychosocial domain. Results: There were no statistically significant associations between estradiol levels and MHR-QOL in univariate analyses (n=455). Multivariable linear regression predicted statistically significant differences in MCS (R2=0.10, P=0.03) and MENQOL-psychosocial domain (R2=0.10, P=0.04), however estradiol was not a significant predictor. Conclusions: This study did not find a statistically significant association between endogenous serum estradiol levels and MHR-QOL in healthy postmenopausal women.

Aim: To describe the predictive validity of reaching low disease activity (LDA) at 1 year on future disability and joint damage in patients with early rheumatoid arthritis (ERA). Methods: First a systematic literature review of prognostic studies assessing the association between disease activity and functional or radiographic outcomes in ERA was performed. Then data from the Study Of New-Onset RA (SONORA) were used to evaluate the impact of year-one LDA on 3-year disability and 2-year radiographic progression using multivariate regression analyses. Results: Our review demonstrated evidence for relationship between baseline disease activity and future disability and join damage. However evidence for the impact of early treatment response on long-term outcomes in ERA is sparse. Analysis of 984 patients showed year one LDA predicts lower HAQ (p<.0001) and less damage (p=0.04) in future. Conclusion: Reaching LDA early is associated with better long-term functional and radiographic outcomes in patients with early RA.

Aim: To describe the predictive validity of reaching low disease activity (LDA) at 1 year on future disability and joint damage in patients with early rheumatoid arthritis (ERA). Methods: First a systematic literature review of prognostic studies assessing the association between disease activity and functional or radiographic outcomes in ERA was performed. Then data from the Study Of New-Onset RA (SONORA) were used to evaluate the impact of year-one LDA on 3-year disability and 2-year radiographic progression using multivariate regression analyses. Results: Our review demonstrated evidence for relationship between baseline disease activity and future disability and join damage. However evidence for the impact of early treatment response on long-term outcomes in ERA is sparse. Analysis of 984 patients showed year one LDA predicts lower HAQ (p<.0001) and less damage (p=0.04) in future. Conclusion: Reaching LDA early is associated with better long-term functional and radiographic outcomes in patients with early RA.

Objective: This thesis aims to construct a framework for studying vitamin D deficiency in young Canadian children. Methods: A practice based research network was created to collect vitamin D data from children 1-5 years of age in Toronto, Canada (TARGet Kids!). A cross-sectional pilot study was completed and a larger study proposed to determine the prevalence and predictors of low vitamin D. Results: The prevalence of low vitamin D (<50nmol/L) in the pilot study was 32% (29/92, 95% CI: 22-42%). Using multivariable linear regression, lower vitamin D level was associated with lower milk volume, higher BMI and watching TV during snacks. A larger study involving 2400 children 1-5 years of age has been proposed. Interpretation: Pilot data has suggested that 30-80% of toddlers in this setting have low vitamin D. A study to clarify these findings and form the basis of a large longitudinal vitamin D cohort has been proposed.

Objective: This thesis aims to construct a framework for studying vitamin D deficiency in young Canadian children. Methods: A practice based research network was created to collect vitamin D data from children 1-5 years of age in Toronto, Canada (TARGet Kids!). A cross-sectional pilot study was completed and a larger study proposed to determine the prevalence and predictors of low vitamin D. Results: The prevalence of low vitamin D (<50nmol/L) in the pilot study was 32% (29/92, 95% CI: 22-42%). Using multivariable linear regression, lower vitamin D level was associated with lower milk volume, higher BMI and watching TV during snacks. A larger study involving 2400 children 1-5 years of age has been proposed. Interpretation: Pilot data has suggested that 30-80% of toddlers in this setting have low vitamin D. A study to clarify these findings and form the basis of a large longitudinal vitamin D cohort has been proposed.

Objective: Describe emergency department (ED) presentations for self-harm by youth (12-17 yearolds), including the mental health follow-up they receive after their first-ever presentation, and analyze the association between this mental health follow-up and repeat presentation(s). Methods: Population-based health services data from Ontario, Canada, covering April 2002 to March 2009, were used to ascertain ED presentations for self-harm by youth (n=16,835). These data were used to create a retrospective cohort (n=3,497) of those making their first-ever presentation, and individually-linked to inpatient admission and ambulatory physician contact data. Mental health follow-up within 30-days of discharge, either from a psychiatrist or from any physician specialty, was assessed. The associations between follow-up and repeat self-harm presentation(s) within the following year were then analyzed. Results: Conservatively, the overall incidence rate for ED presentations for self-harm by Ontario youth was 239.0 per 100,000 person-years. Rates were higher in girls, increased with age and inversely related to neighbourhood income and community size (population). Self-harm made up a small but severe proportion of ED use by youth. Over half (57.2%) making their first-ever self-harm presentation had no mental health contact with a physician within 30 days of discharge (and several demographic, clinical and health service variables were associated with follow-up). However, mental health follow-up was not associated with reduced odds of repetition or fewer repeat presentations. Conclusions: ED presentations for self-harm by youth in Ontario are remarkably consistent with those reported from other Western countries. Self-harm is an important public health issue in Canada and requires a comprehensive prevention strategy. These data suggested follow-up youth received after their first-ever ED presentation for self-harm may be inadequate and strategies to improve follow-up may be needed. Still, more research is needed to establish the effect of follow-up on relevant outcomes.

Objective: Describe emergency department (ED) presentations for self-harm by youth (12-17 yearolds), including the mental health follow-up they receive after their first-ever presentation, and analyze the association between this mental health follow-up and repeat presentation(s). Methods: Population-based health services data from Ontario, Canada, covering April 2002 to March 2009, were used to ascertain ED presentations for self-harm by youth (n=16,835). These data were used to create a retrospective cohort (n=3,497) of those making their first-ever presentation, and individually-linked to inpatient admission and ambulatory physician contact data. Mental health follow-up within 30-days of discharge, either from a psychiatrist or from any physician specialty, was assessed. The associations between follow-up and repeat self-harm presentation(s) within the following year were then analyzed. Results: Conservatively, the overall incidence rate for ED presentations for self-harm by Ontario youth was 239.0 per 100,000 person-years. Rates were higher in girls, increased with age and inversely related to neighbourhood income and community size (population). Self-harm made up a small but severe proportion of ED use by youth. Over half (57.2%) making their first-ever self-harm presentation had no mental health contact with a physician within 30 days of discharge (and several demographic, clinical and health service variables were associated with follow-up). However, mental health follow-up was not associated with reduced odds of repetition or fewer repeat presentations. Conclusions: ED presentations for self-harm by youth in Ontario are remarkably consistent with those reported from other Western countries. Self-harm is an important public health issue in Canada and requires a comprehensive prevention strategy. These data suggested follow-up youth received after their first-ever ED presentation for self-harm may be inadequate and strategies to improve follow-up may be needed. Still, more research is needed to establish the effect of follow-up on relevant outcomes.

Introduction: Trauma centers (TC) are the only institutions with resources to manage patients with severe traumatic brain injury (TBI). We chose to examine potential barriers to access to TC care for TBI patients. Methods: Administrative datasets were used to evaluate access to TC among patients with severe TBI. We examined triage practices of EMS in TBI. Finally, we analyzed surveys to capture the beliefs, perceptions and knowledge of ED physicians with respect to TBI. Results: 57% of patients in Ontario had any access to a TC following TBI. Of patients who had potential access to a TC from the scene of injury as defined by pre-hospital triage guidelines, 60% of patients were undertriaged. Challenges that ED physicians faced with managing TBI, included lack of beds at TC and difficulty attaining transport resources. Conclusion: Access to TC care for patients with TBI is impeded by patient and system level factors.