Enhancing performance in the presence of outliers with redescending M-estimators.

In real-life situations, we have to analyze the data that contains the atypical observations, and the presence of outliers has adverse effects on the performance of ordinary least square estimates. In this situation, redescedning M-estimators, proposed by Huber (1964), are used to tackle the effects of outliers to increase the efficiency of least square estimates. In this study, we introduce a redescending M-estimator designed to generate robust estimates by mitigating the influence of outlier observations, even when the tuning constant is set to low values. This innovative estimator exhibits enhanced linearity at its core and maintains continuity throughout its range. Our proposed estimator stands out for its novelty, simplicity, differentiability, and practical applicability across real-world scenarios. The results of the proposed redescedning M-estimators are compared with existing robust estimators using an extensive simulation study. Two examples based on real-life data are also added to validate the performance of the suggested function. The formulated redescedning M-estimator produced efficient results as compared to all the considered redescedning M-estimators.

Memory type Bayesian adaptive max-EWMA control chart for weibull processes.

The simultaneous monitoring of both the process mean and dispersion has gained considerable attention in statistical process control, especially when the process follows the normal distribution. This paper introduces a novel Bayesian adaptive maximum exponentially weighted moving average (Max-EWMA) control chart, designed to jointly monitor the mean and dispersion of a non-normal process. This is achieved through the utilization of the inverse response function, particularly suitable for processes conforming to a Weibull distribution. To assess the effectiveness of the proposed control chart, we employed the average run length (ARL) and the standard deviation of run length (SDRL). Subsequently, we compared the performance of our proposed control chart with that of an existing Max-EWMA control chart. Our findings suggest that the proposed control chart demonstrates a higher level of sensitivity in detecting out-of-control signals. Finally, to illustrate the effectiveness of our Bayesian Max-EWMA control chart under various Loss Functions (LFs) for a Weibull process, we present a practical case study focusing on the hard-bake process in the semiconductor manufacturing industry. This case study highlights the adaptability of the chart to different scenarios. Our results provide compelling evidence of the exceptional performance of the suggested control chart in rapidly detecting out-of-control signals during the hard-bake process, thereby significantly contributing to the improvement of process monitoring and quality control.

A redescending M-estimator approach for outlier-resilient modeling.

The OLS model is built on the assumption of normality in the distribution of error terms. However, this assumption can be easily violated, especially when there are outliers in the data. A single outlier can disrupt the normality assumption of error terms, making the OLS model less effective. In such situations, M-estimators (MEs) come into play to obtain reliable estimates. We introduce a redescending M-estimators (RME) for robust regression to handle datasets with outliers. The proposed RME produces more robust estimates by effectively managing the influence of outliers, even at lower values of the tuning constant. We compared the performance of this estimator with existing RMEs using real-life data examples and an extensive simulation study. The results show that our suggested RME is more efficient than the compared ME in various situations.

Utilization of Carbon Dioxide Angiography and Percutaneous Balloon Angioplasty for Treatment of Transplant Renal Artery Stenosis.

BACKGROUND: Transplant renal artery stenosis (TRAS) may lead to graft dysfunction and failure. Progressive deterioration of renal allograft function may be exacerbated by contrast-induced nephrotoxicity during iodine contrast administration for renovascular imaging of allografts. We present our institutional experience of endovascular management for TRAS using CO2 digital subtraction angiography (CO2-DSA) and balloon angioplasty to manage failing renal transplants. METHODS: Four patients with renal allografts from March 2017-May 2018 were referred for graft dysfunction and pending renal transplant failure. Indications for referral included refractory hypertension, decreasing renal functioning, and elevated renovascular systolic velocities. RESULTS: Median age of the four patients was 41.5 years (22-60 years). There were two male and female patients. Chronic hypertension and type 2 diabetes mellitus were the most common comorbidities. An average total of 75 mL of CO2 was used, supplemented with 17.4 mL of iodinated contrast. All patients had improvements in renal function following intervention with a mean decrease in systolic and diastolic blood pressure of 25.8% and 21.4%, respectively. We also observed a mean decrease of BUN by 13.6% and creatinine by 37.4%. Additionally, eGFR increased by 37.7%. All allografts survived after surgery, and only one patient required repeat angioplasty for recurrence. CONCLUSIONS: CO2-DSA with balloon angioplasty can be successfully utilized to salvage deteriorating kidney allograft function in patients with TRAS.

Role of single dose antibiotic prophylaxis in clean orthopedic surgery.

OBJECTIVE: To compare the proportion of early postoperative infection in clean orthopedic surgery after single dose of prophylactic antibiotic and multiple doses of prophylactic antibiotic. DESIGN: Interventional quasi-experimental study. PLACE AND DURATION OF STUDY: Department of Orthopedics, Abbasi Shaheed Hospital, Karachi from April 2004 to March 2005. MATERIAL AND METHODS: Two hundred patients of either age and gender, undergoing clean orthopedic surgery were equally divided into two groups A and B. Group A was given single dose of prophylactic antibiotic, while group B was given multiple doses of prophylactic antibiotic. Follow-up period was 28 days. All cases were evaluated for postoperative wound infection. Sampling technique was non-probability convenience. RESULTS: Mean age was 35.51+/-20.79 years in group A and 26.17+/-19.79 years in group B. However, there was a significantly higher proportion of male patients in group B than in group A (p=0.006). Statistical analysis showed no significant difference in the proportion of early postoperative infection cases between the two groups(p=0.270). Staphylococcus aureus was the commonest organism cultured from the wound discharge in our study followed by E. coli. Eight of our cases having postoperative wound infection showed no growth, out of which 7 were superficial and 1 was deep. There was no significant difference between the two groups regarding mean operating time and duration of stay in hospital. CONCLUSION: There was no statistically significant difference in the proportion of early postoperative infection cases between the two groups.

Union and complications after Thomas splint and early hip spica for femoral shaft fractures in children.

OBJECTIVE: To compare the time of union, degree of shortening and angulations in coronal and sagittal plane in children after applying Thomas splint and early hip spica for the treatment of isolated closed femoral shaft fractures. DESIGN: Interventional quasi-experimental study. PLACE AND DURATION OF STUDY: Orthopedic department of Abbasi Shaheed Hospital, Karachi from December 2002 to January 2004. SUBJECTS AND METHODS: A 100 patients of either gender selected by non-probability convenience with closed unilateral femoral shaft fracture were equally divided into 2 groups. Group A was treated with Thomas splint and Group B with early hip spica casting. Above mentioned variables were noted in both groups. RESULTS: In group A, there were 60% (n = 30) males and 40% (n = 20) females. In group B, there were 62% (n = 31) males and 38% (n = 19) females. Mean age was 6.94 + 2.75 years in group A and 5.48 + 2.67 years in group B. Time of union, degree of shortening and angulations in coronal and sagittal plane were not significantly different in two groups. Duration of stay in hospital was 4.82 + 2.4 days in group A and 3.68 + 2.11 days in group B. CONCLUSION: Results comparable to early hip spica cast can be obtained with Thomas splint in children with isolated closed femoral shaft fracture.