Numerous papers have been written to show which combinations of Shewhart-type quality-control charts are optimal for detecting systematic shifts in the mean response of a process, increases in the random error of a process, and linear drift effects in the mean response across the assay batch. One paper by Westgard et al. (Clin Chem 1977;23:1857-67) especially seems to have attracted the attenti...

The sensitivity of four tests on Shewhart type Q-eharis and of specially designed EWMA and CUSUM Q-eharts to detect one-step permanent shifts of either a normal mean or standard deviation has been studied. The usual test that signals for one point beyond three standard deviations on a Shewhart chart is found to have poor sensitivity, generally. The test that signals when four out of five consec...

Introduction The outcome of thyroid surgery is usually assessed according to two major complications: recurrent laryngeal nerve paralysis and hypoparathyroidism. The purpose of the study was to monitor the outcomes of thyroid surgery using Shewhart control charts, and then to identify possible ways to improve quality by exploring the special causes of variation in the observed complication rate...

Mr. Walter Salisbury died suddenly at Northampton on "th January, 1935, at the age of forty-six. He had been suffering from pneumonia following influenza. He entered the Bristol Medical School in 1906, and was a student at the -ftoyal Infirmary, winning the Tibbits Prize for Surgery. He qualified M.B., B.S. London, in 1913, and held the offices ?f House Surgeon and Casualty Officer at the Royal...

Modelling of Walter and Duerbeck’s photoelectric observations of ST Ind is performed. The Wilson-Devinney model along with a Monte Carlo method as the search procedure, was used to derive the physical parameters of this contact system. One dark spot on the surface of the primary component was introduced to explain the observed difference in the heights of the maxima.

This paper presents the economic design of modified X chart for autocorrelated data and comparison with the economic design of Shewhart’s X chart. An attempt has been made to counter autocorrelation by designing the modified X chart; as the cost of operating a process control system is an important element in the economic design of control charts. The economic designs of both modified and Shewh...

Background. Use of statistical process control (SPC) in healthcare is increasing but remains less common than in other industries. Healthcare-associated infections (HAIs) are important applications that can benefit from SPC methods, including use within existing surveillance programs to trigger investigation and intervention. The empirical value of SPC, however, typically is anecdotal and remai...

The influence of the estimation of parameters in Shewhart control charts is investigated. It is shown by simulation and asymptotics that (very) large sample sizes are needed to accurately determine control charts if estimators are plugged in. Correction terms are developed to get accurate control limits for common sample sizes in the in-control situation. Simulation and theory show that the new...