Weibull Proportional Hazards Model Research Articles

Phenotypic relationship between linear descriptive type traits and functional longevity of Holstein cows in different housing systems using a Weibull proportional hazards model

Phenotypic relationship between linear descriptive type traits and functional longevity of Holstein cows in different housing systems using a Weibull proportional hazards model

Practical health indicator construction methodology for bearing ensemble remaining useful life prediction with ISOMAP-DE and ELM-WPHM

To improve the accuracy of our previous bearing ensemble remaining useful life (RUL) prediction model using the genetic algorithm (GA), support vector regression, and the Weibull proportional hazard model (WPHM) (see Qiu et al (2020 Measurement 150 107097)), we proposed a more practical health indicator (HI) construction methodology for bearing ensemble RUL prediction. A weighted coefficient determination method for four prognostic metrics-monotonicity, robustness, trendability, and consistency-was proposed to select sensitive health features accurately using the analytic hierarchy process. The selected sensitive health features were fused through isometric feature mapping (ISOMAP), and differential evolution (DE) was employed to replace GA for computing the optimal weight coefficients of each input fused feature. One-dimensional HI was constructed by multiplying each input fused feature with the corresponding optimal weight coefficient, and RUL prediction was implemented through an extreme learning machine (ELM) and WPHM. The accuracy and effectiveness of the proposed method were validated by a bearing experiment. The results show that HI construction with ISOMAP-DE has achieved the best performance, and the proposed ELM-WPHM model is compared with BP-WPHM, SVM-WPHM, LSTM-WPHM, and DLSTM-WPHM in terms of RMSE criteria. The minimum error and training time appear in ELM-WPHM, indicating the superiority of the proposed bearing ensemble RUL prediction model.

Fleckscore system of exterior evaluation as a more accurate indirect predictor of longevity in Slovak Simmental dairy cows

The goal of the work was to discover the influence of conformation traits evaluated by the Fleckscore system on the length of productive life of Slovak Simmental dairy cows. Evaluation of body conformation traits according to the Fleckscore system was performed on 3 452 cows. The relationship of individual traits to longevity was analysed using the Weibull proportional hazard model. The results confirmed that smaller and longer cows, which were well muscular and with a deeper body, had a lower risk of early culling than cows in the reference group. Hock angularity, pastern and hoof height scored with low or high marks were associated with an early culling of cows. In terms of the length of productive life, a slightly more elastic pattern is required. Cows with a deeper udder and a stronger and tighter fore udder attachment, which were also average in notching and height central ligament and centrally placed teats, reached a longer productive life.

Modeling Pipe Break Data Using Survival Analysis with Machine Learning Imputation Methods

The development of asset life estimation tools based on historical data is essential to the effective management of pipeline assets. One tool that may assist with asset management is survival analysis. However, left-truncated break records pose a challenge in the practice of survival analysis to obtain sound inferences and predictions. In this study, we propose a data-driven approach that integrates machine learning imputation methods with survival analysis. To demonstrate the proposed methodology, we perform a case study using ductile iron (DI) water distribution pipes from an anonymized utility in the midwestern United States. Two artificial neural network (ANN) models are developed as imputation methods to calibrate the survival curves and mean time to first failure (MTTF) estimates from the Weibull proportional hazards model (WPHM). Results show that the MTTF estimation bias is reduced from 14.3% to 2.1% by using imputation as a preceding procedure. Empirical findings show that despite the limited accuracy of imputation models, the use of imputation methods can still improve the survival analysis results and mitigate the impact of left-truncated break records.

Operating Environment effect on Remaining Useful Life Case study: Sungun Copper Mine

The Remaining Useful Life (RUL) valuation of mining machinery is a principal to ensure the production/output and customer satisfaction in the mining zone. In many cases, it may be of attention to know the expected value of the remaining life of the item before it fails from an arbitrary time that known RUL. The system's failure is also evaluated with the reliability index, which describes up-times. An individual unit's reliability during field use is essential in many mining equipment applications. This index, especially in industrial systems, and being affected by the internal condition also affects operating environmental conditions. For example, the loader performance in cold weather will be different from that of warm, which will affect the machine's reliability and thus the RUL. In reliability engineering, operating environmental conditions are considered Risk factors or Covariates. Therefore, in this paper, an approach is proposed first to analyze the system's reliability considering covariates' effect and then estimate the RUL for different scenarios. The proportional hazard model was used in reliability analysis to be realistic and take the operational influencing factors in calculation. Methods are presented for calculating the reliability function and computing the RUL as a function of the current conditions to guarantee the desired output. The remaining useful life estimation of a Komatsu PC-1250 from the Sungun copper mine was evaluated as a case study of this approach. Systems operating environmental factors such as shift, dump-truck kind, rock kind, … (known as covariates) are assumed to influence covariate in this context. As a result, the Weibull proportional hazard model was fitted to describe the failure behavior, and the RUL of four selected scenarios was evaluated. Presented results can be used, e.g., for developing operational performance, planning of maintenance activities, spare parts provision, and the profitability of the owner of an asset.

Effect of Calving Difficulties and Calf Mortality on Functional Longevity in Polish Holstein-Friesian Cows.

Simple SummaryLongevity, or the length of a cow’s productive life, is important in terms of profitability, animal welfare and environmental sustainability. In genetic evaluations, interest focuses on functional longevity, defined as a cow’s ability to avoid forced culling, an ability that increases the possibility of voluntary disposal based on economic criteria. Longevity is affected by several non-productive functional traits, among them those related to calving performance: calving ease (dystocia) and perinatal calf mortality (stillbirth). Parturition is a critical event in a cow’s life that has a number of different short- and long-term consequences. In the Polish Holstein-Friesian population, the incidence of dystocia and stillbirth is within the lower range of frequencies found in other dairy cattle populations. Our research showed that both traits affect functional longevity. Difficult calvings occur more frequently in heifers and increase the risk of involuntary culling more than in later parturitions. Additionally, a higher risk of culling is related to birth of a male calf. Moreover, the negative impact of calf mortality on longevity is also more pronounced in primiparous cows and in the case of delivery of male calves. Reducing the incidence of calving problems and perinatal mortality may improve the longevity of dairy cows.Longevity is one of the functional traits that considerably affect dairy herd profitability. A Weibull proportional hazards model was used to evaluate the impact of difficult calvings and calf stillbirths on cow functional longevity, defined as length of productive life corrected for milk production. The data for analysis comprised calving ease and calf mortality scores of 2,163,426 calvings, 34.4% of which came from primiparous cows. The percentage of male calves was 53.4%. Calving ease was scored as “without assistance” (34.44%), “with assistance” (62.03%), “difficult—hard pull” (3.39%), and “very difficult, including caesarean section” (0.14%). Calf mortality scores were “live born” (94.21%) and “stillborn or died within 24 h” (5.79%). The Weibull proportional hazards model included classes of calving ease or calf mortality scores × parity (1, ≥2) × sex of calf as time-dependent fixed effect. The model also included time-dependent fixed effects of year × season, parity × stage of lactation, annual change in herd size, fat yield and protein yield, time-independent fixed effect of age at first calving, and time dependent random herd × year × season. In first-parity cows, very difficult birth of a bull or heifer increased the relative risk of culling, respectively, 2.18 or 1.26 times as compared with calving without assistance. In later parities, the relative risk of culling related to very difficult calving was 2.0 times (for male calves) and 1.33 times (for female calves) higher than the relative risk of culling associated with calving without assistance. Calf mortality showed a negative impact on longevity in both heifers and cows. First-parity stillbirth increased the relative risk of culling depending on sex of calf by 18% in females and by 15% in males; in later parities the increase of the relative risk of culling was lower (by 7% for females, 9% for males). Difficult calvings and their consequences, especially in primiparous cows, may negatively influence dairy herd profitability by reducing the length of cows’ productive life.

Dynamic Metabolic Risk Profiling of World Trade Center Lung Disease: A Longitudinal Cohort Study.

Rationale: Metabolic syndrome (MetSyn) increases the risk of World Trade Center (WTC) lung injury (LI). However, the temporal relationship of MetSyn, exposure intensity, and lung dysfunction is not well understood. Objective: To model the association of longitudinal MetSyn characteristics with WTC lung disease to define modifiable risk. Methods: Firefighters, for whom consent was obtained (N = 5,738), were active duty on September 11, 2001 (9/11). WTC-LI (n = 1,475; FEV1% predicted <lower limit of normal [LLN]) and non-WTC-LI (n = 4,263; FEV1% predicted ⩾LLN at all exams) was the primary outcome, and FVC% predicted <LLN and FEV1/FVC <0.70 were secondary outcomes. We assessed 1) the effect of concurrent MetSyn on longitudinal lung function by linear mixed models, 2) the temporal effect of MetSyn and exposure by Weibull proportional hazards, 3) the effects of MetSyn's rate of change by two-stage models, and 4) the nonlinear joint effect of longitudinal MetSyn components by a partially linear single-index model (PLSI). Measurements and Main Results: WTC-LI cases were more often ever-smokers, arrived in the morning (9/11), and had MetSyn. Body mass index ⩾30 kg/m2 and high-density lipoprotein <40 mg/dl were most contributory to concurrent loss of FEV1% predicted and FVC% predicted while conserving FEV1/FVC. Body mass index ⩾30 kg/m2 and dyslipidemia significantly predicted WTC-LI, FVC% predicted <LLN in a Weibull proportional hazards model. Dynamic risk assessment of WTC-LI on the basis of MetSyn and exposure showed how reduction of MetSyn factors further reduces WTC-LI likelihood in susceptible populations. PLSI demonstrates that MetSyn has a nonlinear relationship with WTC lung disease, and increases in cumulative MetSyn risk factors exponentially increase WTC-LI risk. An interactive metabolic-risk modeling application was developed to simplify PLSI interpretation. Conclusions: MetSyn and WTC exposure contribute to the development of lung disease. Dynamic risk assessment may be used to encourage treatment of MetSyn in susceptible populations. Future studies will focus on dietary intervention as a disease modifier.

Optimal stratification of survival data via Bayesian nonparametric mixtures

The stratified proportional hazards model represents a simple solution to take into account heterogeneity within the data while keeping the multiplicative effect of the predictors on the hazard function. Strata are typically defined a priori by resorting to the values of a categorical covariate. A general framework is proposed, which allows the stratification of a generic accelerated lifetime model, including, as a special case, the Weibull proportional hazards model. The stratification is determined a posteriori, taking into account that strata might be characterized by different baseline survivals, and also by different effects of the predictors. This is achieved by considering a Bayesian nonparametric mixture model and the posterior distribution it induces on the space of data partitions. An optimal stratification is then identified following a decision theoretic approach. In turn, stratum-specific inference is carried out. The performance of this method and its robustness to the presence of right-censored observations are investigated through an extensive simulation study. Further illustration is provided analysing a data set from the University of Massachusetts AIDS Research Unit IMPACT Study.

Surgeon Factors Have a Larger Effect on Vascular Access Type and Outcomes than Patient Factors

Though patient factors are frequently linked to hemodialysis vascular access selection and outcomes, variability by surgeon and surgeon specialty may play a role as well. The objective of this study is to examine the extent to which individual surgeons influence selection of vascular access type, removal of tunneled hemodialysis catheter (THC), and repeat vascular access. A national claims database was used to identify patients initiating hemodialysis via a THC between 2011 and 2017. Likelihood of repeat AVF/AVG was analyzed using mixed-effects logistic regression. Time from initial arteriovenous fistula (AVF)/graft (AVG) to THC removal and time to repeat AVF/AVG were analyzed using Weibull proportional hazard models. Individual surgeon identifier served as the random effect in all models. 6,908 AVF/AVG met the inclusion criteria: 5366 (78%) AVF and 1,542 (22%) AVG. Surgeon specialty only had a significant influence on access type, with vascular surgeons having 26% greater odds of performing AVG compared to general surgeons (P=0.006). Relative to the other independent variables, individual surgeon identifier had the greatest magnitude of effect on access type (median odds ratio, 2.36; 95% CI, 2.09-2.72). Individual surgeon identifier had the second greatest magnitude of effect likelihood of THC removal (median hazard ratio, 1.66; 95% CI, 1.58-1.77) and second access (median hazard ratio, 1.83; 95% CI, 1.66-2.05), in both cases second only to the effect of AVG, which was associated with greater likelihood of THC removal (hazard ratio 1.91; 95% CI, 1.77-2.07) and lower likelihood of second access (hazard ratio 0.44; 95% CI, 0.38-0.52). Individual surgeons are associated with greater variation in vascular access type and likelihood of repeat access than surgeon specialty and measurable patient demographics/co-morbidities. Future research should focus on identifying which surgeon factors are associated with improved outcomes.

Determinants of the Age at First Marriage among the University Teachers in Algeria: A mix Methodology Approach

This study examines the determinants of age at first marriage among the university teachers in Algeria. A Weibull proportional hazard and multivariable logistic regressions models were used on data set from a survey covering a sample of 682 teachers. The findings revealed that: The median ages at first marriage are: 36 and 39.4 years for men and women, respectively, with a gap of 3.1 and 8 years from the general population. For: birth order, teacher specialty, study place and working before joining the academic staff all together explain a very small percent of the variation of the age at marriage; in contrast, Housing, salaries’ level, and a suitable partner were the hidden factors determining the age at marriage. As policy implications, policy-makers have to focus on these factors in order to help teachers to satisfy this biological and sociological need.&#x0D; JEL Classification: C4; J12

Evaluation of the body conformation traits by system FleckScore and its relationship to longevity of Slovak Simmental cows

Article Details: Received: 2020-10-28 | Accepted: 2020-11-27 | Available online: 2021-01-31 https://doi.org/10.15414/afz.2021.24.mi-prap.155-158 The study is focused to analyse of the relationship between composite type traits evaluated by new system Fleckscore and functional length of productive life in the Slovak Simmental cows. All cows was scored in the first parity just because 85% data were censored. The score of frame, feet and legs, muscularity and udder was between 68 and 93 points.The lowest risk of culling was found for muscularity (0.591) at the group scored between 84 and 93 points,for udder (0.879) and feet and legs (0.751) scored between 77 - 79 points and for frame (0.816) at the score 80 points. Rate of culled cows on first or second parity was 15 %. Within this group, diseases and fertility disorders (involuntary culling) represented 23 % culling cows. Keywords: body conformation trait, FleckScore, longevity, survival analysis References Ansari-Lari, M. et al. (2012). Causes of culling in dairy cows and its relation to age at culling and interval from calving in Shiraz, Southern Iran. Veterinary Research Forum , 3(4), 233–237. https://doi.org/ 4313041 Anzenberger, H. (2012). Zweitbewertung im neuen System. Rinderzucht Fleckvieh , 3(1), 28–29. Ducrocq, V. et al. (2012). The survival Kit v6.1. User´s Manual . 83 p. Frelich, J. et al. (2010). Reasons for the culling of dairy cows on low-input mountain farms. Journal of Agrobiology , 27(1), 41–48. https://doi.org/10.2478/s10146-009-0006-z Imbayarwo-Chikosi, V. E. et al. (2016). Impact of comformation traits on functional longevity in South African Holstein cattle. Animal Production Science , 58(3) 481–488. Morek-Kopec´, M. and Zarnecki, A. (2012). Relationship between conformation traits and longevity in Polish Holstein Friesian cattle. Livestock Science , 149(1-2) 53–61. https://doi.org/ 10.1016/j.livsci.2012.06.022 Novotný, L. et al. (2017). Genetic Relationship between Type Traits, Number of Lactations Initiated, and Lifetime Milk Performance in Czech Fleckvieh Cattle. Czech Journal of Animal Science , 62(12), 501–510. https://doi.org/ 10.17221/60/2017-CJAS Ondrakova, M. (2014). Fleckscore proposal for second and third lactations. Zpravodaj chovatelu a plemenne knihy ceskeho strakateho skotu , 2. 10–12. (in Czech) Sawa, A. et al. (2013). Relationship between Conformation Traits and Lifetime Production Efficiency of Cows. International Scholarly Research Notices , vol. 2013, Article ID 124690, 4 p. https://doi.org/10.1155/2013/124690 Sewalem, A. et al. (2004). Analysis of the Relationship Between Type Traits and Functional Survival in Canadian Holsteins Using a Weibull Proportional Hazards Model. Journal of Dairy Science , 87, 3938–3946. https://doi.org/10.3168/jds.S0022-0302(04)73533-X Tanzler, J. (2014). Lineare Nachzuchtbewertung mit Fleckscore. Fleckviehzucht in Osterreich, 4, 25–27. Zavadilova, L. et al. (2011). Effect of type traits on functional longevity of Czech Holstein cows estimated from a Cox proportional hazards model. Journal of Dairy Science , 94, 4090–4099. https://doi.org/10.3168/jds.2010-3684

Cardiovascular mortality and cardiovascular event rates in patients with inflammatory rheumatic diseases in the CARdiovascular in rheuMAtology (CARMA) prospective study-results at 5 years of follow-up.

To determine cardiovascular (CV) mortality and incidence of the first CV event (CVE) in patients with chronic inflammatory rheumatic diseases (CIRD) after 5 years of follow-up. This is an analysis of the CARdiovascular in rheMAatology (CARMA) study after 5 years of follow-up. It includes patients with RA (n = 775), AS (n = 738) and PsA (n = 721), and individuals without CIRD (n = 677) attending outpatient rheumatology clinics from 67 public hospitals in Spain. Descriptive analyses were performed for the CV mortality at 5 years. The Systematic COronary Risk Evaluation (SCORE) function at 5 years was calculated to determine the expected risk of CV mortality. Poisson models were used to estimate the incidence rates of the first CVE. Hazard ratios of the risk factors involved in the development of the first CVE were evaluated using the Weibull proportional hazard model. Overall, 2382 subjects completed the follow-up visit at 5 years. Fifteen patients died due to CVE. CV deaths observed in the CIRD cohort were lower than that predicted by SCORE risk charts. The highest incidence rate of CVE [7.39 cases per 1000 person-years (95% CI 4.63, 11.18)] was found in PsA patients. However, after adjusting for age, sex and CV risk factors, AS was the inflammatory disease more commonly associated with CVE at 5 years [hazard ratio 4.60 (P=0.02)], compared with those without CIRD. Cardiovascular mortality in patients with CIRD at 5 years of follow-up is lower than estimated. Patients with AS have a higher risk of developing a first CVE after 5 years of follow-up.

Genetic analysis of survival potential of Boer x Central Highland goats under semi-intensive management

Kid survival is very critical to be profitable in goat production. Thus, this study was conducted to identify genetic and non-genetic factors affecting the survival rate of Boer x Central Highland goat and to estimate genetic parameters for survival using linear animal and Weibull proportional hazard model. Data collected from the Sirinka goat breeding station were utilized for this study. Survival analysis was conducted with a Weibull proportional hazard model using Survival Kit version 6.1 software. The genetic parameters for survival traits were estimated using both Survival Kit fitted sire model and ASREML software fitted animal model with logit function. Four models for survival traits were fitted in order to optimize the model for each trait in the animal model. The log-likelihood ratio test was used for selecting the best-fitted model. The proportion of right-censored kids up to 3, 6 and 12 months of age was 77.8, 66.2 and 57.9 %, respectively. From the total death, about 73.1 % of death occurred up to 140 days of age. Gastrointestinal parasites, septicemia, pneumonia are the leading causes of death. Birth type, birth weight, dam breed and year of birth are the most important risk factors for kid mortality. Based on selected linear animal models, total heritability (h2t) estimates for the survival of kids at 3, 6 and 12 months of age were 0.006, 0.096 and 0.098, respectively. The maternal permanent environmental effect explains 6% of the phenotypic variation in survival up to weaning age. However, the impact of the maternal effect on post-weaning survival was found to be negligible. The genetic correlation between birth weight and survival to yearling age was 0.55 ± 0.15. The heritability estimates for survival at 3, 6 and 12 months of age from the Weibull proportional hazard model were 0.10, 0.13 and 0.18, respectively. As both pre- and post-weaning survival traits are economically important traits, including in the selection index of the breeding program would be paramount. Besides selection, using a local goat as a dam line and improving management in the flock would be an option to improve the survival of kids.

Survival analyses in Holstein cows considering direct disease diagnoses and specific SNP marker effects

The aim of the present study was to infer influences of health disorders and of specific SNP markers on longevity in Holstein cows via survival analyses. Longevity was defined as the length of productive life (LPL), reflecting the interval from first calving until the culling or censoring date. In this regard, we considered longevity records from 129,386 Holstein cows from 57 large-scale herds, with calving dates in first parity between January 2004 and December 2017 (30.27% censored records). We selected specific diseases from the overall categories claw disorders, udder diseases, metabolic disorders, and female fertility disorders within 3 stages of parities 1, 2, and 3. Lactation stage 1 was the period from calving to days in milk (DIM) 59, lactation stage 2 from DIM 60 to DIM 299, and lactation stage 3 from DIM 300 to the next calving date. The effects of the diseases on culling risk ratios were estimated via Weibull proportional hazards models. In this regard, we used 3 different modeling strategies. In modeling strategy M1S, binary diseases from different parities and lactation stages for the same diagnosis were modeled as explanatory variables in separate runs. Modeling strategy M3S included diseases for the same diagnosis from stage 1, 2, and 3 in the same parity simultaneously. Modeling strategy M9S implied consideration of diseases for the same diagnosis from different lactation stages and from all 3 parities simultaneously. The effect of the same diseases on culling risks from M1S and M3S were similar, with increasing detrimental effect of diseases recorded in later lactation stages and parities. The strongest disease effect on LPL was detected for clinical and subclinical mastitis recorded in the middle of the third lactation, with culling risks of 2.59 and 2.40, respectively, and for claw disorders from the last stage in third lactation (culling risks in the range from 1.85 to 2.29). The effective (ignoring the proportion of censoring; heff2) and equivalent (considering proportion of censoring; hequ2) heritabilities for LPL when considering diseases from specific stages in parities 1 and 3 were quite low ( heff2 0.02 - 0.17; hequ2 0.01 - 0.12). Simultaneous consideration of same disease diagnoses across stages (M3S) and across lactations (M9S) contributed to a LPL heritability increase. Ignoring diseases as explanatory variables in survival analyses was generally associated with a decline of genetic LPL variances and LPL heritabilities. A genome-wide association study for LPL was based on estimated de-regressed proofs from 17,362 genotyped cows. Six SNP located on Bos taurus autosomes 1, 4, 10, 13, and 28 were significantly associated with LPL (using a 5% false discovery rate). Gene annotations via Ensembl identified the 4 potential candidate genes ETV1, ONECUT1, MACROD2, and SIRT1, which directly (via disease resistance mechanisms) or indirectly (via milk productivity) influence dairy cow longevity. Genotypes of the 6 significantly associated SNP were considered as fixed effects in Weibull hazards models, but their effects on culling risks were nonsignificant. Heritabilities for LPL from all SNP-based survival models considering the single SNP separately or the 6 SNP simultaneously were 0.05 (hequ2) and 0.12 (heff2). The small number of significantly associated SNP in genome-wide associations and the minor effect of specific SNP on LPL in survival analyses underline the polygenetic nature of longevity.

Lifetime cumulative incidence of dementia in a community-dwelling elderly population in Japan.

ObjectiveTo estimate the lifetime cumulative incidence of dementia and its subtypes from a community-dwelling elderly population in Japan.MethodsA total of 1,193 community-dwelling Japanese individuals without dementia, aged 60 years or older, were followed up prospectively for 17 years. The cumulative incidence of dementia was estimated based on a death- and dementia-free survival function and the hazard functions of dementia at each year, which were computed by using a Weibull proportional hazards model. The lifetime risk of dementia was defined as the cumulative incidence of dementia at the point in time when the survival probability of the population was estimated to be less than 0.5%.ResultsDuring the follow-up, 350 participants experienced some type of dementia; among them, 191 participants developed Alzheimer disease (AD) and 117 developed vascular dementia (VaD). The lifetime risk of dementia was 55% (95% confidence interval, 49%–60%). Women had an approximately 1.5 times greater lifetime risk of dementia than men (65% [57%–72%] vs 41% [33%–49%]). The lifetime risks of developing AD and VaD were 42% (35%–50%) and 16% (12%–21%) in women vs 20% (7%–34%) and 18% (13%–23%) in men, respectively.ConclusionLifetime risk of all dementia for Japanese elderly was substantial at approximately 50% or higher. This study suggests that the lifetime burden attributable to dementia in contemporary Japanese communities is immense.

A Front-Line and Cost-Effective Model for the Assessment of Service Life of Network Pipes

In any water utility, a reliable assessment of the service life of the network pipes is a key piece within the big puzzle of assets management. This paper presents a new statistical model (basic pipes life assessment, BPLA) to assess the service life of pipes, to locate the pipes on the failures bath curve and to forecast the expected failures in future years. Its main novelties are the processing of pipe information (is that information what is adapted to the classical maintenance engineering and not the other way back) and the definition of two different time variables that can be analyzed in parallel. The first novelty makes the model less demanding in terms of data and software tools than others currently available, and the second one allows to get all the results after one single stage of calculation. To show its usability, the BPLA has been applied to a pipe network that supplies water to 500,000 citizens for which two years of failure records are available. Procedures and results have been compared to the well-known Weibull proportional hazard model (WPHM), with final relative errors lower than 10% and 15% on each particular result.

Comparative Analysis of the Cox Semi-parametric and Weibull Parametric Models on Colorectal Cancer Data

The survival and hazard functions are key concepts in survival analysis for describing the distribution of event times. The survival function gives, for every time, the probability of surviving (or not experiencing the event). The hazard function gives the potential that the event will occur, per time unit, given that an individual has survived up to the specified time. While these are often of direct interest, many other quantities of interest (e.g., median survival) may subsequently be estimated from knowing either the hazard or survival function. This research was a five-year retrospective study on data from a record of colorectal cancer patients that received treatments from 2013 to 2017 in Radiotherapy Department of Usmanu Danfodiyo University Teaching Hospital, Sokoto, being it one of the cancer registries in Nigeria. 9 covariates were selected to fit colorectal cancer data using Cox and Weibull Regression Models. From the result it is concluded that the predictor variables could significantly predict the survival of colorectal cancer patients using Cox. Also the result of the Weibull Proportional Hazard Model shows that the model is adequate enough to predict the survival of the colorectal patients. The A. I. C result shows that, according to our colorectal cancer data, the semi-parametric Cox regression model performed better than the parametric Weibull proportional hazards model. However, in the present study, the Cox model provided an efficient and a better fit to the study data than Weibull model.

Predictive maintenance of systems subject to hard failure based on proportional hazards model

The remaining useful lifetime (RUL) estimated from the in-situ degradation data has shown to be useful for online predictive maintenance. In the literature, the RUL is often estimated by assuming a soft-failure threshold for the degradation data. In practice, however, systems may not be subject to the degradation-induced soft failures. Instead, the systems are deemed to be fail when they cannot perform the intended function, and such failures are known as hard failures. Because there are no fixed thresholds for hard failures, the corresponding RUL estimation is not an easy task, which causes difficulties in finding the optimal maintenance schedule. In this study, a Weibull proportional hazards model is proposed to jointly model the degradation data and the failure time data. The degradation data are treated as the time-varying covariates so that the degradation does not directly lead to system failures, but increases the hazard rate of hard failures. A random-effects Wiener process is proposed to model the degradation data by considering the system heterogeneities. Based on the developed proportional hazards model, closed-form distribution of the RUL is derived upon each inspection and the optimal maintenance schedule is then obtained by minimizing the system maintenance cost. The proposed maintenance strategy is successfully applied to predictive maintenance of lead-acid batteries.

Geographical variations of the associations between health interventions and all-cause under-five mortality in Uganda

BackgroundTo reduce the under-five mortality (U5M), fine-gained spatial assessment of the effects of health interventions is critical because national averages can obscure important sub-national disparities. In turn, sub-national estimates can guide control programmes for spatial targeting. The purpose of our study is to quantify associations of interventions with U5M rate at national and sub-national scales in Uganda and to identify interventions associated with the largest reductions in U5M rate at the sub-national scale.MethodsSpatially explicit data on U5M, interventions and sociodemographic indicators were obtained from the 2011 Uganda Demographic and Health Survey (DHS). Climatic data were extracted from remote sensing sources. Bayesian geostatistical Weibull proportional hazards models with spatially varying effects at sub-national scales were utilized to quantify associations between all-cause U5M and interventions at national and regional levels. Bayesian variable selection was employed to select the most important determinants of U5M.ResultsAt the national level, interventions associated with the highest reduction in U5M were artemisinin-based combination therapy (hazard rate ratio (HRR) = 0.60; 95% Bayesian credible interval (BCI): 0.11, 0.79), initiation of breastfeeding within 1 h of birth (HR = 0.70; 95% BCI: 0.51, 0.86), intermittent preventive treatment (IPTp) (HRR = 0.74; 95% BCI: 0.67, 0.97) and access to insecticide-treated nets (ITN) (HRR = 0.75; 95% BCI: 0.63, 0.84). In Central 2, Mid-Western and South-West, largest reduction in U5M was associated with access to ITNs. In Mid-North and West-Nile, improved source of drinking water explained most of the U5M reduction. In North-East, improved sanitation facilities were associated with the highest decline in U5M. In Kampala and Mid-Eastern, IPTp had the largest associated with U5M. In Central1 and East-Central, oral rehydration solution and postnatal care were associated with highest decreases in U5M respectively.ConclusionSub-national estimates of the associations between U5M and interventions can guide control programmes for spatial targeting and accelerate progress towards mortality-related Sustainable Development Goals.

Analysis of drug-induced hearing loss by using a spontaneous reporting system database.

Many drugs can cause hearing loss, leading to sensorineural deafness. The aim of this study was to evaluate the risk of drug-induced hearing loss (DIHL) by using the Japanese Adverse Drug Event Report (JADER) database and to obtain profiles of DIHL onset in clinical settings. We relied on the Medical Dictionary for Regulatory Activities preferred terms and standardized queries, and calculated the reporting odds ratios (RORs). Furthermore, we applied multivariate logistic regression analysis, association rule mining, and time-to-onset analysis using Weibull proportional hazard models. Of 534688 reports recorded in the JADER database from April 2004 to June 2018, adverse event signals were detected for platinum compounds, sulfonamides (plain) (loop diuretics), interferons, ribavirin, other aminoglycosides, papillomavirus vaccines, drugs used in erectile dysfunction, vancomycin, erythromycin, and pancuronium by determining RORs. The RORs of other aminoglycosides, other quaternary ammonium compounds, drugs used in erectile dysfunction, and sulfonamides (plain) were 29.4 (22.4–38.6), 18.5 (11.2–30.6), 15.4 (10.6–22.5), and 12.6 (10.0–16.0), respectively. High lift score was observed for patients with congenital diaphragmatic hernia treated with pancuronium using association rule mining. The median durations (interquartile range) for DIHL due to platinum compounds, sulfonamides (plain), interferons, antivirals for treatment of hepatitis C virus (HCV) infections, other aminoglycosides, carboxamide derivatives, macrolides, and pneumococcal vaccines were 25.5 (7.5–111.3), 80.5 (4.5–143.0), 64.0 (14.0–132.0), 53.0 (9.0–121.0), 11.0 (3.0–26.8), 1.5 (0.3–11.5), 3.5 (1.3–6.8), and 2.0 (1.0–4.5), respectively. Our results demonstrated potential risks associated with several drugs based on their RORs. We recommend to closely monitor patients treated with aminoglycosides for DIHL for at least two weeks. Moreover, individuals receiving platinum compounds, sulfonamides (plain), interferons, and antivirals for HCV infection therapy should be carefully observed for DIHL for at least several months.