Univariate X̄ control charts for individual characteristics in a multinormal model

The early work on multivariate statistical process control was built upon Hotelling's T2 control chart which was developed to simultaneously monitor the means of correlated quality variables. This chart, however, has a drawback, namely, the problem of identifying the responsible variable(s) when an out-of-control signal occurs. One alternative is to use a separate X̄ control chart for each individual characteristic with equal risks, based on Bonferroni inequality. In this study, we show that, from an economic perspective, it may be desirable to have unequal type I risks for the individual charts, because of different inspection and restoration costs associated with each variable. We obtain their risk ratios, which are measures of relative importance of the variables monitored. Then, based on these risk ratios, we develop computer algorithms for finding the exact control limits for individual variables from a multinormal distribution, in the sense that the overall type I risk of the charts is equal to the desired value. Numerical studies show that the proposed methods give optimal or near-optimal results from an economic as well as statistical point of view

The single surgeon learning curve of laparoscopic liver resection : a continuous evolving process through stepwise difficulties

The aim of the study was to evaluate the single-surgeon learning curve (SSLC) in laparoscopic liver surgery over an 11-year period with risk-adjusted (RA) cumulative sum control chart analysis.Laparoscopic liver resection (LLR) is a challenging and highly demanding procedure. No specific data are available for defining the feasibility and reproducibility of the SSLC regarding a consistent and consecutive caseload volume over a specified time period.A total of 319 LLR performed by a single surgeon between June 2003 and May 2014 were retrospectively analyzed. A difficulty scale (DS) ranging from 1 to 10 was created to rate the technical difficulty of each LLR. The risk-adjusted cumulative sum control chart (RA-CUSUM) analysis evaluated conversion rate (CR), operative time (OT) and blood loss (BL). Perioperative morbidity and mortality were also analyzed.The RA-CUSUM analysis of the DS identified 3 different periods: P1 (n = 91 cases), with a mean DS of 3.8; P2 (cases 92-159), with a mean DS of 5.3; and P3 (cases 160-319), with a mean DS of 4.7. P2 presented the highest conversion and morbidity rates with a longer OT, whereas P3 showed the best results (P<0.001). Fifty cases were needed to achieve a significant decrease in BL. The overall morbidity rate was 13.8%; no perioperative mortality was observed.According to our analysis, at least 160 cases (P3) are needed to complete the SSLC performing safely different types of LLR. A minimum of 50 cases can provide a significant decrease in BL. Based on these findings, a longer learning curve should be anticipated to broaden the indications for LLR

Predicting subsequent contralateral slipped capital femoral epiphysis: an evidence-based approach.

PurposeThe purpose of this study was to identify risk factors for developing a subsequent contralateral slipped capital femoral epiphysis (SCFE) and provide a prediction score to quantify risk of subsequent slip at the time of initial presentation.MethodsThis retrospective study included patients that presented with a unilateral SCFE between 2006 and 2017. Chart and radiographic review were performed to collect demographic, clinical and radiographic risk factors. Descriptive statistics, univariate analyses and multivariate regression analysis were used to compare risk factors between patients that did or did not develop a subsequent contralateral SCFE.ResultsThis study included 183 patients and 33 patients (18%) developed a subsequent contralateral SCFE. Younger age at time of initial presentation, lower modified Oxford Score and smaller difference in epiphyseal-diaphyseal angle between both sides during index presentation were significant predictors of subsequent contralateral SCFE. Specifically, age ≤ 11 years, modified Oxford Score ≤ 20 and difference in epiphyseal-diaphyseal angle of ≤ 21° between both hips were predictive of a contralateral slip (Area Under the Curve = 0.78; p &lt; 0.05). The presence of each risk factor increased the risk of subsequent contralateral SCFE and having all three risk factors increased the risk to 73%.ConclusionThere is a significant risk of subsequent contralateral SCFE in patients with unilateral SCFE, and predictive risk factors include younger age, lower modified Oxford Score and smaller difference in epiphyseal-diaphyseal angle between the affected and unaffected hips.Level of evidenceLevel III

Incidence and predictors of premature ventricular complexes following catheter ablation for atrial fibrillation

BACKGROUND: Atrial fibrillation (AF) is the most common cardiac arrhythmia, and previous studies have focused on the epidemiology, mechanisms and risk factors for this global disease (Ryder and Benjamin 1999). Various studies have examined the mechanism, epidemiology, and risk factors for AF. One of the most common triggers for AF is believed to be premature atrial contractions (PACs) usually arising from the pulmonary veins of the left atrium, but the relationship between AF and premature ventricular complexes (PVCs) is not well understood. Studies investigating the triggers of premature beats in both the atria and ventricles are similar, so it is possible that treatment for one arrhythmia may affect the incidence of another. It is hypothesized that due to commonly shared mechanisms of triggered activity or automaticity between PACs and PVCs, and shared risk factors, that patients with AF undergoing treatment with catheter ablation may be prone to develop PVCs. OBJECTIVE: To investigate the incidence of clinically detected PVCs among patients undergoing catheter ablation for AF, and clinical predictors of PVC development in this cohort of patients. We also aim to evaluate if incident PVC detection is associated with recurrent AF following AF ablation in a cohort of 317 patients receiving treatment at a single academic medical center. METHODS: A total of 375 patients undergoing AF ablation from 2009-2012 were reviewed, and patients that underwent repeat ablations were excluded, yielding 317 patients for analysis. T-tests and Chi-squared analyses were used in univariate analyses to test for significance between characteristics of AF patients who did and did not develop PVCs. Kaplan-Meier analyses and Cox proportional hazards models were used for univariate and multivariate survival analyses, respectively, to assess the risks of incident PVC development. RESULTS: Of 317 patients with AF undergoing pulmonary vein isolation (PVI) ablation, 36.3% developed clinically detectable PVCs following ablation. A history of clinically evident PVC prior to catheter ablation for AF was associated with an 80% increase in risk of incident PVC development (HR=1.83, 95% CI 1.02-3.26, p=0.041). Additionally, a history of prior angioplasty, stent, or percutaneous coronary intervention (PCI) was associated with a 73% decreased risk of incident PVCs (HR=0.27, 95% CI 0.08-0.88, p=0.03). In patients with a history of PVC prior to ablation, or who developed PVCs after ablation, there was no significant difference in the risk of AF recurrence (HR=1.01, 95% CI 0.70-1.46, p=0.96; and HR=1.09, 95% CI 0.78-1.53, p=0.60, respectively). CONCLUSIONS: Over 1 in 3 patients develop clinically detected PVCs following catheter ablation. Predictors of incident PVC development include a history of PVC, whereas a history of angioplasty, stent, or PCI was associated with less incident PVC development. Furthermore, there was no significant association between both a history of PVC or incident PVC and risk of recurrent AF following ablation

Barriers to Mitigation: A Pilot Study

This pilot research was undertaken to discover barriers that prevent homeowners from mitigating earthquake hazards in their homes. There is a relatively significant body of literature on disaster mitigation, which is reviewed and summarized in this report. However, no studies address how these barriers may be overcome so that homeowners would be more proactive in mitigation. If the barriers can be identified, then future communications and policy actions that address these barriers can be taken, resulting in more widespread mitigation implementation that reduces the injury and damage potential that communities face, leading to a reduction in the post-disaster response requirement, and the time required to achieve recovery. Data came from an online survey of San José State University employees; the survey took approximately 15 minutes for respondents to complete. Questions addressed home characteristics, demographic characteristics, perceptions of earthquake risk, levels of mitigation, past experience with earthquake injury or damage, social influences on hazard and damage prevention, and reactions to various incentives. Statistical analyses were done using SPSS version 16.0. Of the total 331 respondents, 215 were homeowners and consequently used for data analysis. Of these homeowners, 79 % owned single-family homes. The sample overwhelmingly expects a major earthquake to occur within the next 10 years, and most expect to suffer earthquake-caused injuries and damage within their homes in the near future. The findings indicate the importance of earthquake expectations and the social network for influencing mitigation. Physical proximity to others who experienced earthquake damage and relational closeness to those who have taken mitigation actions were found to have a positive effect on mitigation implementation by individuals. Homeowners assumed responsibility for mitigation, and cost is generally not a concern. The most prevalent obstacles to mitigation were the feeling that the mitigation is not necessary or that it is inconvenient. Home structures and systems mitigation is far more commonplace than home contents mitigation. Mitigation of home contents was perceived as not being very important, and this perception prevents individuals from taking mitigation actions. All incentive types that were presented to respondents, which were primarily financial in nature, were reported as likely to increase mitigation. Providing advice and information was also reported to likely result in higher levels of mitigation. The development of mitigation approaches that are low-cost and simple is expected to have a positive effect on mitigation actions. In addition, codes were found to be effective at prompting mitigation – most respondents had mitigated for items that have code requirements. One outcome of this is that mitigation of structures is more widely reported than mitigation of home contents. More research is needed to explore non-financial incentives for mitigation, including incentives provided by personal relationships and how social relationships may be leveraged. There is also a need to explore whether different types of incentives (such as free labor or education) would be more or less effective at prompting particular mitigation actions (such as securing the foundation or strapping down appliances). It would be helpful to take a “bottom up” approach by conducting focus groups on these topics. Demographic effects on mitigation and barriers to mitigation also need to be explored further. There were suggestions that demography mattered, but the sample size for this survey was not sufficiently large to draw statistically valid conclusions. There is also a need to revise the survey instrument to remove some ambiguities and inadequacies that currently exist. It would be useful to explore why persons might have taken particular mitigation actions and how social networks affect their mitigation action, among other things. Heightened perceptions of earthquake threats, experience with earthquake injuries and damage, and social relationships are critical predictors of mitigation. Individuals who know others who have mitigated are more likely to mitigate; therefore improved communications, on the personal level, on the topic of mitigation can be effective. Given the perceptions of mitigating home contents, the public also needs to be made more aware of the threats posed by home contents during an earthquake

Poisson regression charts for the monitoring of surveillance time series

This paper presents a Poisson control chart for monitoring time series of counts typically arising in the surveillance of infectious diseases. The in-control mean is assumed to be time-varying and linear on the log-scale with intercept and seasonal components. If a shift in the intercept occurs the system goes out-of-control. Novel is that the magnitude of the shift does not have to be specified in advance: using the generalized likelihood ratio (GLR) statistic a monitoring scheme is formulated to detect on-line whether a shift in the intercept occurred. For this specific Poisson chart the necessary quantities of the GLR detector can be efficiently computed by recursive formulas. Extensions to more general Poisson charts e.g. containing an autoregressive epidemic component are discussed. Using Monte Carlo simulations run length properties of the proposed schemes are investigated. The practicability of the charts is demonstrated by applying them to the observed number of salmonella hadar cases in Germany 2001-2006

The Impact of poor glycaemic control on the prevalence of erectile dysfunction in men with type 2 Diabetes Mellitus: A Systematic Review.

To determine the impact of poor glycaemic control on the prevalence of erectile dysfunction among men with type 2 Diabetics aged 27 to 85 years.The databases Embase classic+Embase, Global health, Ovid Medline and PsychINFO, were searched for relevant studies in June 2014 using the keywords: (Diabetes Mellitus OR diabetes mellitus type2 OR DM2 OR T2DM OR insulin resistance) AND (erectile dysfunction OR sexual dysfunction OR impotence) AND glycaemic control.All study settings were considered (primary care, secondary care and tertiary care setting).Type 2 Diabetic Patients with erectile dysfunction.Included studies must include one of the following outcomes: (1) HBA1c for assess the level of glycaemic control; (2) Erectile dysfunction (any stage: IIEF-5 = 21 or less).Five cross-sectional studies involving 3299 patients were included. The findings pointed to a positive association between erectile dysfunction and glycaemic control. Three studies showed a significant positive association, while one study showed only a weak correlation and one study showed borderline significance. Patients age, diabetes mellitus duration, peripheral neuropathy and body mass index had positive association with erectile dysfunction. However, smoking and hypertension were not associated with erectile dysfunction in most included studies. Physical activity had a protective effect against erectile dysfunction.We may conclude that the risk of erectile dysfunction is higher in type 2 diabetic men with poor glycaemic control than those with good control

Nonparametric control charts for bivariate high-quality processes

For attribute data with (very) low rates of defectives, attractive control charts can be based on the maximum of subsequent groups of r failure times, for some suitable r≥1, like r=5. Such charts combine good performance with often highly needed robustness, as they allow a nonparametric adaptation already for Phase I samples of ordinary size. In the present paper we address the problem of extending this approach to the situation where two characteristics have to be monitored simultaneously. Generalization to the multivariate case is straightforward