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Selected AbstractsANTISOCIAL BEHAVIOR AND YOUTH GANG MEMBERSHIP: SELECTION AND SOCIALIZATIONCRIMINOLOGY, Issue 1 2004RACHEL A. GORDON We examine whether gang membership is associated with higher levels of delinquency because boys predisposed to delinquent activity are more likely than others to join. We use 10 years of longitudinal data from 858 participants of the Pittsburgh Youth Study to identify periods before, during and after gang membership. We build on prior research by controlling for ages and calendar time, by better accounting for gang memberships that occurred before the study began, and by using fixed effects statistical models. We find more evidence than has been found in prior studies that boys who join gangs are more delinquent before entering the gang than those who do not join. Even with such selective differences, however, we replicate research showing that drug selling, drug use, violent behaviors and vandalism of property increase significantly when a youth joins a gang. The delinquency of peers appears to be one mechanism of socialization. These findings are clearest in youth self-reports, but are also evident in reports from parents and teachers on boys' behavior and delinquency. Once we adjust for time trends, we find that the increase in delinquency is temporary, that delinquency falls to pre-gang levels when boys leave gangs. [source] Modelling the effects of air pollution on health using Bayesian dynamic generalised linear modelsENVIRONMETRICS, Issue 8 2008Duncan Lee Abstract The relationship between short-term exposure to air pollution and mortality or morbidity has been the subject of much recent research, in which the standard method of analysis uses Poisson linear or additive models. In this paper, we use a Bayesian dynamic generalised linear model (DGLM) to estimate this relationship, which allows the standard linear or additive model to be extended in two ways: (i) the long-term trend and temporal correlation present in the health data can be modelled by an autoregressive process rather than a smooth function of calendar time; (ii) the effects of air pollution are allowed to evolve over time. The efficacy of these two extensions are investigated by applying a series of dynamic and non-dynamic models to air pollution and mortality data from Greater London. A Bayesian approach is taken throughout, and a Markov chain monte carlo simulation algorithm is presented for inference. An alternative likelihood based analysis is also presented, in order to allow a direct comparison with the only previous analysis of air pollution and health data using a DGLM. Copyright © 2008 John Wiley & Sons, Ltd. [source] Serum levels of vitamin D, PTH and calcium and breast cancer risk,a prospective nested case,control studyINTERNATIONAL JOURNAL OF CANCER, Issue 9 2010Martin Almquist Abstract Previous studies indicate that calcium and its regulating hormones, i.e., parathyroid hormone (PTH) and vitamin D, might affect breast cancer risk. Evidence also suggests that this relationship could be influenced by menopausal status and BMI. We examined breast cancer risk related to prediagnostic serum levels of vitamin D (25OHD2 and 25OHD3), PTH and calcium using a nested case,control design within the Malmö Diet and Cancer Study. There were 764 incident breast cancer cases, and 764 controls were selected by incidence density matching, using age as the underlying time scale, matching on calendar time at inclusion, menopausal status and age at inclusion. Using logistic regression analysis, odds ratios (OR) with 95% confidence intervals were calculated for breast cancer risk in different quartiles of the analyzed factors. All analyses were adjusted for risk factors for breast cancer, and for levels of albumin, creatinine and phosphate. Analyses were repeated stratified for BMI and menopausal status, and for low vs. high levels of 25OHD3, PTH and calcium. There was a weak, nonsignificant inverse association between breast cancer risk and 25OHD3, and the OR for the 2nd, 3rd and 4th quartiles, as compared to the first, were 0.84 (0.60,1.15), 0.84 (0.60,1.17) and 0.93 (0.66,1.33). Serum calcium was positively associated with breast cancer in premenopausal women (OR for the 4th quartile = 3.10:1.33,7.22 and p for quartile trend = 0.04), and in women with BMI > 25 (OR for the 4th quartile = 1.94:1.12,3.37 and p for trend < 0.01). There was no association between baseline serum PTH and breast cancer risk. [source] A Complete Decomposition of Unemployment Dynamics using Longitudinal Grouped Duration Data,OXFORD BULLETIN OF ECONOMICS & STATISTICS, Issue 1 2005Muriel Dejemeppe Abstract In this paper, we study the unemployment dynamics in the Belgian regions, Flanders and Wallonia, on the basis of aggregate stratified data covering the period 1973,93. We decompose the aggregate exit probability from unemployment into calendar time and, both observed and unobserved, compositional effects. We find that changes in the inflow composition affect the cyclical fluctuations in unemployment duration only marginally. However, the long-run improvement in the quality of entrants into unemployment, notably in terms of educational attainment, mitigates the strong upward trend in this duration. This is a new result as none of the existing studies purges the trend in the aggregate outflow rate of the variation in its composition. We also conclude that in Belgium, incidence explains as much as 45% of the evolution of unemployment. Finally, the diverging evolution of unemployment across Flanders and Wallonia predominantly results from a stronger decline in the exit rates from unemployment in Wallonia. [source] Chronic statin therapy and the risk of colorectal cancer,PHARMACOEPIDEMIOLOGY AND DRUG SAFETY, Issue 9 2008MSCE, Yu-Xiao Yang MD Abstract Background and Aims Epidemiologic studies on a potential chemopreventive effect of statin therapy have yielded conflicting results. We sought to clarify whether long-term statin therapy has a chemopreventive effect on the risk of colorectal cancer (CRC) in a large, population-representative cohort. Methods A nested case,control study was conducted among patients ,50 years of age and with ,5 years of CRC-free initial follow-up in the General Practice Research Database (GPRD; 1987,2002). Cases consisted of all patients with incident CRC. Up to 10 controls were matched with each case on practice site and both duration and calendar time of follow-up prior to the index date. The primary exposure of interest was ,5 years of cumulative statin use. Results We identified 4432 incident CRC cases and 44,292 controls. The adjusted odds ratio (OR) for ,5 years of statin exposure was 1.1 (95% confidence interval (CI): 0.5,2.2). Chronic NSAID/aspirin use did not modify this primary association (test for interaction, p,=,0.5). Compared to statin non-users, the adjusted OR for 10 years of statin exposure was 1.3 (95% CI: 0.6,2.7), and the adjusted OR associated with the highest quartile of cumulative statin dose was 1.2 (95% CI: 0.9,1.7). There was a non-statistically significant trend towards a possible reduction in CRC risk among users of high daily statin dose. Conclusion Long-term statin therapy at usual doses was not associated with a significantly reduced risk of CRC. A chemopreventive effect at high daily doses cannot be excluded. Copyright © 2008 John Wiley & Sons, Ltd. [source] Antihypertensive drug therapy and the risk of lower extremity amputations in pharmacologically treated type 2 diabetes patients,PHARMACOEPIDEMIOLOGY AND DRUG SAFETY, Issue 3 2004Joëlle A. Erkens PharmD Abstract Purpose The objective of this study was to determine the association between different antihypertensive drug therapies and lower extremity amputations (LEAs) in type 2 diabetes patients. Methods Data were obtained from the PHARMO Record Linkage System comprising pharmacy records and data on hospitalisations for all 450,000 residents of eight Dutch cities. In a nested case-control study among 12,140 type 2 diabetes patients who used antihypertensive drugs, 26 cases with a first LEA and 94 controls without a LEA matched on age, sex and calendar time were identified. Logistic regression was used to estimate the relative risk of LEA and to adjust for potential confounding factors. Results Among type 2 diabetes patients who used antihypertensive drugs, subjects who used thiazide diuretics, alone or in combination, had a higher risk of LEA compared to subjects who used Angiotensin Converting Enzyme (ACE) inhibitor monotherapy (crude odds ratio (OR): 6.11 [95% confidence interval (CI): 1.32,28.27]). The use of thiazide diuretics was also associated with an increased risk of LEA when compared to the use of any non-thiazide antihypertensive drug (adjusted OR: 7.04 [1.10,45.30]). The increased risk of LEA associated with the use of thiazides compared to the use of non-thiazides depended on the duration of use (adjusted OR,365 days, 4.82 [0.61,38.34] and adjusted OR>365 days, 26.16 [1.02,674.02], p -trend,=,0.01). Conclusions Treatment with thiazide diuretics compared to treatment with other antihypertensive drugs was associated with excess amputations in type 2 diabetes patients. Due to several limitations of this study, our findings do not preclude the use of thiazides in type 2 diabetes mellitus patients as yet. Copyright © 2004 John Wiley & Sons, Ltd. [source] Cancer incidence rates among Lawrence Livermore National Laboratory (LLNL) employees: 1974,1997,AMERICAN JOURNAL OF INDUSTRIAL MEDICINE, Issue 1 2004M. Donald Whorton MD Abstract Background In the mid-1970's an excess of malignant melanoma of the skin was noted among employees at the Lawrence Livermore National Laboratory (LLNL). A 1984 cancer incidence study showed a non-significant excess of total cancers among female employees with significant excesses for melanoma, rectum and anus, and salivary gland cancers. For male employees, there was a non-significant deficit of total cancer with significant excesses in melanoma and non-brain nervous system cancers. This paper reports the results of a surveillance effort to update our understanding of the patterns of cancer incidence in this population. Methods We used California Cancer Registry (CCR) data to ascertain employees who had worked for six or more consecutive months at LLNL during the 24-year period of 1974 through 1997 who were diagnosed weith cancer during that time frame. We used the Standardized Incidence Ratio (SIR) in our analyses. Results There were 17,785 employees who provided 186,558 person-years of observation: 145,203 were from males and 41,355 were from females. The CCR, through its linkage techniques, identified 541 individuals with invasive cancer and 96 with in situ cancer. A total of 404 males had invasive cancer and 33 had in situ cancer whereas there were 137 females with invasive cancer and 63 with in situ cancer. The SIR for invasive cancer in males was 69 (95% CI 62,76). The overall cancer SIR for males was unaffected by calendar time. There were only two invasive cancer sites with significant excess: melanoma and cancer of the testes. For eight categories or cancer sites, we found a statistical deficit in cancer incidence. The most striking deficit occurred in cancer of the lungs and bronchus with a SIR of 36 (95% CI 26,50). The SIR for invasive cancer in females was 80 (95% CI 67,94). The overall cancer SIR for females decreased over calendar time. There was a statistically significant deficit for cancers of the female genital organs. There were 84 cases of invasive and in situ melanoma in both genders. Time-trend analyses for melanoma showed a significant excess during the years 1974,1985 but a reduction to community rates from 1986 through 1997. There were 21 individuals with testicular cancer with a SIR of 207 (95% CI 129,317). There were no differences in age at diagnosis or cell type with the comparison population. We analyzed the data using the same radiosensitive cancer categories used in the 1984 study. There were no increases in SIRs in any of these categories. Conclusions We found that the LLNL employees had less cancer than expected with males having relatively fewer cancers than females. The lung cancer rate for males was remarkably low. Since 1986 the melanoma rates resemble the community rates. Testicular cancer rates are modestly elevated and appear to have been so for the past 20 years. Lifestyle patterns, including smoking, and cancer screening activities are probably important contributors to the observed low cancer rates. Am. J. Ind. Med. 45:24,33, 2004. © 2003 Wiley-Liss, Inc. [source] Proportional Intensity Models Robustness with Overhaul IntervalsQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 3 2006Shwu-Tzy Jiang Abstract The class of semi-parametric proportional intensity (PI) models applies to recurrent failure event modeling for a repairable system with explanatory variables (covariates). Certain repairable systems (e.g. aircraft and electrical power generating plants) experience a substantial period of downtime due to performing maintenance (i.e. major overhaul) at scheduled intervals or following a major failure. Other systems (e.g. emergency power units) experience extended periods of non-operating dormancy. These discontinuities in observation time have potential effects on the accuracy of estimation for covariate effects, particularly where calendar time is the life metric. This paper examines the robustness of two PI methods (Prentice,Williams,Peterson gap time (PWP-GT) and Andersen,Gill (AG)) as a function of the overhaul or dormancy duration. The PWP-GT model proves to perform well for sample size of 60 (30 per level of a class covariate), constant or moderately decreasing/increasing rate of occurrence of failures, and relative overhaul (dormancy) durations less than half of the immediately preceding interval between failures. The AG model performs consistently well for a small sample size of 20 (10 per level of a class covariate) for homogeneous Poisson processes, regardless of the relative overhaul (dormancy) duration. Copyright © 2005 John Wiley & Sons, Ltd. [source] Could accelerated aging explain the excess mortality in patients with seropositive rheumatoid arthritis?ARTHRITIS & RHEUMATISM, Issue 2 2010Cynthia S. Crowson Objective To determine whether the mortality pattern in patients with seropositive rheumatoid arthritis (RA) is consistent with the concept of accelerated aging, by comparing the observed mortality rates in patients with RA with the age-accelerated mortality rates from the general population. Methods A population-based inception cohort of patients with seropositive RA (according to the American College of Rheumatology 1987 criteria) was assembled and followed up for vital status until July 1, 2008. The expected mortality rate was obtained by applying the death rates from the general population to the age, sex, and calendar year distribution of the RA population. The observed mortality was estimated using Kaplan-Meier methods. Acceleration factors for the expected mortality were estimated in accelerated failure time models. Results A total of 755 patients with seropositive RA (mean age 55.6 years, 69% women) were followed up for a mean of 12.5 years, during which 315 patients died. The expected median survival was age 82.4 years, whereas the median survival of the RA patients was age 76.7 years. Results of statistical modeling suggested that, in terms of mortality rates, patients with RA were effectively 2 years older than actual age at RA incidence, and thereafter the patients underwent 11.4 effective years of aging for each 10 years of calendar time. Conclusion The overall observed mortality experience of patients with seropositive RA is consistent with the hypothesis of accelerated aging. The causes of accelerated aging in RA deserve further investigation. [source] |