Comparison of proportional hazards and accelerated failure time models

The field of survival analysis has experienced tremendous growth during the latter half of the 20th century. The methodological developments of survival analysis that have had the most profound impact are the Kaplan-Meier method for estimating the survival function, the log-rank test for comparing the equality of two or more survival distributions, and the Cox proportional hazards (PH) model for examining the covariate effects on the hazard function. The accelerated failure time (AFT) model was proposed but seldom used. In this thesis, we present the basic concepts, nonparametric methods (the Kaplan-Meier method and the log-rank test), semiparametric methods (the Cox PH model, and Cox model with time-dependent covariates) and parametric methods (Parametric PH model and the AFT model) for analyzing survival data. We apply these methods to a randomized placebo-controlled trial to prevent Tuberculosis (TB) in Ugandan adults infected with Human Immunodificiency Virus (HIV). The objective of the analysis is to determine whether TB preventive therapies affect the rate of AIDS progression and survival in HIV-infected adults. Our conclusion is that TB preventive therapies appear to have no effect on AIDS progression, death and combined event of AIDS progression and death. The major goal of this paper is to support an argument for the consideration of the AFT model as an alternative to the PH model in the analysis of some survival data by means of this real dataset. We critique the PH model and assess the lack of fit. To overcome the violation of proportional hazards, we use the Cox model with time-dependent covariates, the piecewise exponential model and the accelerated failure time model. After comparison of all the models and the assessment of goodness-of-fit, we find that the log-logistic AFT model fits better for this data set. We have seen that the AFT model is a more valuable and realistic alternative to the PH model in some situations. It can provide the predicted hazard functions, predicted survival functions, median survival times and time ratios. The AFT model can easily interpret the results into the effect upon the expected median duration of illness for a patient in a clinical setting. We suggest that the PH model may not be appropriate in some situations and that the AFT model could provide a more appropriate description of the data

Possible Luttinger liquid behavior of edge transport in monolayer transition metal dichalcogenide crystals.

In atomically-thin two-dimensional (2D) semiconductors, the nonuniformity in current flow due to its edge states may alter and even dictate the charge transport properties of the entire device. However, the influence of the edge states on electrical transport in 2D materials has not been sufficiently explored to date. Here, we systematically quantify the edge state contribution to electrical transport in monolayer MoS2/WSe2 field-effect transistors, revealing that the charge transport at low temperature is dominated by the edge conduction with the nonlinear behavior. The metallic edge states are revealed by scanning probe microscopy, scanning Kelvin probe force microscopy and first-principle calculations. Further analyses demonstrate that the edge-state dominated nonlinear transport shows a universal power-law scaling relationship with both temperature and bias voltage, which can be well explained by the 1D Luttinger liquid theory. These findings demonstrate the Luttinger liquid behavior in 2D materials and offer important insights into designing 2D electronics

Energy auditing and energy conservation potential for glass works

A state-owned glass production enterprise introduces the strategic investor to carry on the assets reorganization, including the purchase of two float glass production lines with subsequent technology transformations and the construction of a new float glass production line with domestic leading technology. The fuel consumption structure has changed from coal-burning to natural gas or fuel oil. The following auditing procedures were followed according to Chinese national standards. These procedures include constituting an ordinance on energy management, strengthening the energy measurement and data statistical system, and improving production lines as well as energy-saving measures. Production scale expanded approximately twice during the period of audit. Comprehensive energy consumption was 2.58 ton coal equivalent (tce) at aqual in heat value (AHV refers to energy consumed to generate each kW h of electric power, each m3 of oxygen, nitrogen, hydrogen, or each kg of steam. The term of AHV provides a unification measurement criterion for fossil fuels consumed before the energy transformation.) account per 10,000 Yuan output value, and 2.17 tce at heat value equivalent (HVE) account. Comprehensive energy consumption per unit of product was 15.35 kg coal equivalent (kce) per weight box. The percentage of energy cost among total cost reduced from 51.19% in 2007 to 46.48% in 2008. Consequently, the comprehensive energy conversion level holds a leading position among peers in China.Assets reorganization Energy consumption Energy management Energy consumption target Energy-saving potential

An external evaluation of a peer-run outreach-based syringe exchange in Vancouver, Canada

Objective: Vancouver, Canada has been the site of an epidemic of human immunodeficiency virus (HIV) among injection drug users (IDU). In response, the Vancouver Area Network of Drug Users (VANDU) initiated a peer-run outreach-based syringe exchange programme (SEP) called the Alley Patrol. We conducted an external evaluation of this programme, using data obtained from the Vancouver Injection Drug Users Study (VIDUS). Methods: Using generalised estimating equations (GEE) we examined the prevalence and correlates of use of the SEP among VIDUS participants followed from 1 December 2000 to 30 November 2003. Results: Of 854 IDU, 233 (27.3%) participants reported use of the SEP during the study period. In multivariate GEE analyses, service use was positively associated with living in unstable housing (Adjusted Odds Ratio [AOR] = 1.83, 95% Confidence Interval [CI]: 1.39 – 2.40), daily heroin injection (AOR = 1.31, 95% CI: 1.01 – 1.70), daily cocaine injection (AOR = 1.34, 95% CI: 1.03 – 1.73), injecting in public (AOR = 3.07, 95% CI: 2.32 – 4.06), and negatively associated with needle reuse (AOR = 0.65, 95% CI: 0.46 – 0.92). Conclusion: The VANDU Alley Patrol SEP succeeded in reaching a group of IDU at heightened risk for adverse health outcomes. Importantly, access to this service was associated with lower levels of needle reuse. This form of peer-based SEP may extend the reach of HIV prevention programmes by contacting IDU traditionally underserved by conventional syringe exchange programmes.Graduate and Postdoctoral StudiesMedicine, Faculty ofOther UBCNon UBCMedicine, Department ofReviewedFacultyResearcherOthe

Drug-related risks among street youth in two neighborhoods in a Canadian setting

We compared drug-related behaviors, including initiation of drug use, among street youth residing in two adjacent neighborhoods in Vancouver. One neighborhood, the Downtown Eastside (DTES), features a large open-air illicit drug market. In multivariate analysis, having a primary illicit income source (adjusted odds ratio [AOR]=2.64, 95% confidence interval [CI]: 1.16–6.02) and recent injection heroin use (AOR=4.25, 95% CI: 1.26–14.29) were positively associated with DTES residence, while recent non-injection crystal methamphetamine use (AOR: 0.39, 95% CI: 0.16–0.94) was negatively associated with DTES residence. In univariate analysis, dealing drugs (odds ratio [OR]=5.43, 95% CI: 1.24–23.82) was positively associated with initiating methamphetamine use in the DTS compared to the DTES. These results demonstrate the importance of considering neighborhood variation when developing interventions aimed at reducing drug-related harms among street-involved youth at various levels of street entrenchment.Medicine, Faculty ofOther UBCMedicine, Department ofPopulation and Public Health (SPPH), School ofReviewedFacultyResearche

Hunger and associated harms among injection drug users in an urban Canadian setting

Background: Food insufficiency is often associated with health risks and adverse outcomes among marginalized populations. However, little is known about correlates of food insufficiency among injection drug users (IDU). Methods: We conducted a cross-sectional study to examine the prevalence and correlates of self-reported hunger in a large cohort of IDU in Vancouver, Canada. Food insufficiency was defined as reporting "I am hungry, but don't eat because I can't afford enough food". Logistic regression was used to determine independent socio-demographic and drug-use characteristics associated with food insufficiency. Results: Among 1,053 participants, 681 (64.7%) reported being hungry and unable to afford enough food. Self-reported hunger was independently associated with: unstable housing (adjusted odds ratio [AOR]: 1.68, 95% confidence interval [CI]: 1.20 - 2.36, spending ≥ $50/day on drugs (AOR: 1.43, 95% CI: 1.06 - 1.91), and symptoms of depression (AOR: 3.32, 95% CI: 2.45 - 4.48). Conclusion: These findings suggest that IDU in this setting would likely benefit from interventions that work to improve access to food and social support services, including addiction treatment programs which may reduce the adverse effect of ongoing drug use on hunger.Medicine, Department ofMedicine, Faculty ofReviewedFacult

Public crack cocaine smoking and willingness to use a supervised inhalation facility: implications for street disorder

Background: The health risks of crack cocaine smoking in public settings have not been well described. We sought to identify factors associated with public crack smoking, and assess the potential for a supervised inhalation facility to reduce engagement in this behavior, in a setting planning to evaluate a medically supervised crack cocaine smoking facility. Methods Data for this study were derived from a Canadian prospective cohort of injection drug users. Using multivariate logistic regression we identified factors associated with smoking crack cocaine in public areas. Among public crack smokers we then identified factors associated with willingness to use a supervised inhalation facility. Results Among our sample of 623 people who reported crack smoking, 61% reported recently using in public locations. In multivariate analysis, factors independently associated with public crack smoking included: daily crack cocaine smoking; daily heroin injection; having encounters with police; and engaging in drug dealing. In sub analysis, 71% of public crack smokers reported willingness to use a supervised inhalation facility. Factors independently associated with willingness include: female gender, engaging in risky pipe sharing; and having encounters with police. Conclusion We found a high prevalence of public crack smoking locally, and this behavior was independently associated with encounters with police. However, a majority of public crack smokers reported being willing to use a supervised inhalation facility, and individuals who had recent encounters with police were more likely to report willingness. These findings suggest that supervised inhalation facilities offer potential to reduce street-disorder and reduce encounters with police.Medicine, Department ofPopulation and Public Health (SPPH), School ofNon UBCMedicine, Faculty ofReviewedFacult

Interest in low-threshold employment among people who inject illicit drugs : implications for street disorder

Background Income generation opportunities available to people who use illicit drugs have been associated with street disorder. Among a cohort of injection drug users (IDU) we sought to examine street-based income generation practices and willingness to forgo these sources of income if other low-threshold work opportunities were made available. Methods Data were derived from a prospective community recruited cohort of IDU. We assessed the prevalence of engaging in disorderly street-based income generation activities, including sex work, drug dealing, panhandling, and recycling/salvaging/vending. Using multivariate logistic regressions based on Akaike information criterion and the best subset selection procedure, we identified factors associated with disorderly income generation activities, and assessed willingness to forgo these sources of income during the period of November 2008 to July 2009. Results Among our sample of 874 IDU, 418 (48%) reported engaging in a disorderly income generation activity in the previous six months. In multivariate analyses, engaging in disorderly income generation activities was independently associated with high intensity stimulant use, as well as binge drug use, having encounters with police, being a victim of violence, sharing used syringes, and injecting in public areas. Among those engaged in disorderly income generation, 198 (47%) reported a willingness to forgo these income sources if given opportunities for low-threshold employment, with sex workers being most willing to engage in alternative employment. Conclusion Engagement in disorderly street-based income generation activities was associated with high intensity stimulant drug use and various markers of risk. We found that a high proportion of illicit drug users were willing to cease engagement in these activities if they had options for causal low-threshold employment. These findings indicate that there is a high demand for low-threshold employment that may offer important opportunities to reduce drug-related street disorder and associated harms.Medicine, Faculty ofOther UBCNon UBCMedicine, Department ofReviewedFacultyResearche