Multivariate semiparametric control charts for mixed-type data.

A useful tool that has gained popularity in the Quality Control area is the control chart which monitors a process over time, identifies potential changes, understands variations, and eventually improves the quality and performance of the process. This article introduces a new class of multivariate semiparametric control charts for monitoring multivariate mixed-type data, which comprise both continuous and discrete random variables (rvs). Our methodology leverages ideas from clustering and Statistical Process Control to develop control charts for MIxed-type data. We propose four control chart schemes based on modified versions of the KAy-means for MIxed LArge KAMILA data clustering algorithm, where we assume that the two existing clusters represent the reference and the test sample. The charts are semiparametric, the continuous rvs follow a distribution that belongs in the class of elliptical distributions. Categorical scale rvs follow a multinomial distribution. We present the algorithmic procedures and study the characteristics of the new control charts. The performance of the proposed schemes is evaluated on the basis of the False Alarm Rate and in-control Average Run Length. Finally, we demonstrate the effectiveness and applicability of our proposed methods utilizing real-world data.

Generalizations of Runs and Patterns Distributions for Sequences of Binary Trials.

In the present paper we study the distributions of families of patterns which generalize runs and patterns distributions extensively examined in the literature during the last decades. In our analysis we assume that the sequence of outcomes under investigation includes independent, but not necessarily identically distributed trials. An illustration is also provided how our new results could be exploited to enrich a new system, still in research, related to patients' weaning from mechanical ventilation.

Hospitalization rates for cholelithiasis and acute cholecystitis doubled for the aged population in Greece over the past 30 years.

OBJECTIVE: Gallbladder disease is becoming increasingly prevalent in Western countries and is a common cause of hospitalization. The objective of this study was to determine time trends in cholelithiasis and acute cholecystitis for hospitalization and disease case fatality in Greece between 1970 and 1998. MATERIAL AND METHODS: Data were obtained from the Annual Bulletin for the Social Welfare and Health Statistics of the National Statistics Service of Greece. Percentage changes in time trends were estimated by comparing the median values of the initial (1970-78) to the last (1989-98) 10-year study period for cholelithiasis and acute cholecystitis at discharge and for all deaths attributed to the disease. RESULTS: Over the study period, age-standardized hospitalization rates for cholelithiasis increased. The median hospitalization rate between the initial and last (178 and 258 per 100,000 of the population, respectively) 10-year study period increased by 44.7%, but peaked to 70.1% and 208.3% for the 70-79 and >80 years age groups, respectively. Case fatality rate declined by 56.8% and the median value was 0.24 per 100 patients hospitalized during the last 10-year period. CONCLUSIONS: Hospitalization rates for cholelithiasis and/or acute cholecystitis increased by 45%, and doubled for elderly patients, while the case fatality rate of the disease halved in Greece over the past 30 years.