The Modified Mixed Exponentially Weighted Moving Average-Cumulative Sum Control Charts for Autocorrelated Process

Statistical Process Control (SPC) is an efficient methodology for monitoring, managing, analysing and recuperating process performance. Implementation of SPC in industries results in biggest benefits, as enhanced quality products and reduced process variation. While dealing with the theory of control chart we generally move with the assumption of independent process observation. But in practice usually, for most of the processes the observations are autocorrelated which degrades the ability of control chart application. The loss caused by autocorrelation can be obliterated by making modifications in the traditional control charts. The article presented here refers to a combination of EWMA and CUSUM charting techniques supplementing modifications in the control limits. The performance of the referred scheme is measured by comparing average run length (ARL) with existing control charts. Also, the referred scheme is found reasonably well for detecting particularly smaller displacements in the process.

Risk-adjusted zero-inflated Poisson CUSUM charts for monitoring influenza surveillance data

Background The influenza surveillance has been received much attention in public health area. For the cases with excessive zeroes, the zero-inflated Poisson process is widely used. However, the traditional control charts based on zero-inflated Poisson model, ignore the association between influenza cases and risk factors, and thus may lead to unexpected mistakes when implementing monitoring charts. Method In this paper, we proposed risk-adjusted zero-inflated Poisson cumulative sum control charts, in which the risk factors were put to adjust the risk of influenza and the adjustment was made by zero-inflated Poisson regression. We respectively proposed the control chart monitoring the parameters individually and simultaneously. Results The performance of our proposed risk-adjusted zero-inflated Poisson cumulative sum control chart was evaluated and compared with the unadjusted standard cumulative sum control charts in simulation studies. The results show that for different distribution of impact factors and different coefficients, the risk-adjusted cumulative sum charts can generate much less false alarm than the standard ones. Finally, the influenza surveillance data from Hong Kong is used to illustrate the application of the proposed chart. Conclusions Our results suggest that the adjusted cumulative sum control chart we proposed is more accurate and credible than the unadjusted standard control charts because of the lower false alarm rate of the adjusted ones. Even the unadjusted control charts may signal a little faster than the adjusted ones, the alarm they raise may have low credibility since they also raise alarm frequently even the processes are in control. Thus we suggest using the risk-adjusted cumulative sum control charts to monitor the influenza surveillance data to alert accurately, credibly and relatively quickly.

Quality control of ultrasonography markers for Down’s syndrome screening: a retrospective study by the laboratory

Objectives Quality control of ultrasonography markers is necessary to ensure greater efficacy of prenatal aneuploidy screening. The aim of this study was to assess the quality of the crown-rump length (CRL) and nuchal translucence (NT) measurement accuracy by the laboratory according to quality indicators. Methods Retrospective observational study on 4,908 single-foetus pregnant women who underwent prenatal aneuploidy screening in the first trimester of pregnancy. Euploid foetuses with CRL between 45 and 84 mm were included, while those with NT≥3.5 mm were excluded. CRL measurement was considered to be accurate if the median multiples of the median (MoM) for pregnancy-associated plasma protein A (PAPP-A) was between 0.90 and 1.10. Fifteen sonographers participated in the study, six of whom comprised the control group. Systematic error for a sonographer was considered when CRL measurement was greater than ±2 mm with respect to the control group. Quality for NT was assured by means of the WHIRI method and each sonographer cumulative sum control chart (CUSUM). Results For CRL accuracy, five sonographers underestimated the measurements, while another four overestimated them, with no statistical differences. For smaller sized foetuses, all sonographers met the established specifications. Regarding NT control, three sonographers did not meet the quality criteria for the median MoM. All sonographers met the specifications for the logarithmic standard deviation of the NT MoM levels. Thirteen sonographers met the CUSUM specifications. Conclusions Evaluation of a quality control of ultrasonography parameters by laboratory professionals is necessary to avoid under- or overestimation tendencies for CRL and NT measurements. CUSUM is a useful tool for the immediate correction of errors in NT measurements.

P70 Investigating the current state of practice for reporting on surgeon's learning and the learning curve in IDEAL studies of surgical innovation: A systematic review

Introduction Community learning is a key component for the progression of surgical innovation, which is itself crucial to advancing surgical practice. Assessment of learning curve’s (LCs) allow rigorous evaluation of new surgical procedures/devices and their introduction into clinical practice. The Idea–Development–Exploration–Assessment–Long-term (IDEAL) framework provides recommendations for the evaluation of new surgical procedures and devices throughout the stages of innovation. This study aimed to identify the current reporting practice of LCs in IDEAL studies. Methods A systematic review was conducted to identify author-reported IDEAL/IDEAL-D studies of any IDEAL stage and surgical specialty. Included were primary studies citing any of 10 key IDEAL papers. Data were extracted including information relating to surgeons’ experience and training, support and performance monitoring, and methods for measuring and assessing the LC. Results Searches yielded 1411 publications, of which 59 studies met the eligibility criteria. Some 31/59 (53%) studies reported information on the LC, however, only 3 (5%) studies measured or reported on LC in detail. These 3 papers included statistical methods (cumulative sum control charts, Shewhart control charts and multivariate analysis). Some 21/59 (36%) studies reported training for surgeons and 16 (27%) reported support or performance monitoring. Conclusion Reporting of the LC or factors influencing LC such as training, was found to be poor in the included studies. Development of more detailed guidance for measuring and reporting the LC in future studies is recommended to facilitate robust evaluation of new surgical procedures and devices.

Monitoring the Zero-Inflated Time Series Model of Counts with Random Coefficient

In this research, we consider monitoring mean and correlation changes from zero-inflated autocorrelated count data based on the integer-valued time series model with random survival rate. A cumulative sum control chart is constructed due to its efficiency, the corresponding calculation methods of average run length and the standard deviation of the run length are given. Practical guidelines concerning the chart design are investigated. Extensive computations based on designs of experiments are conducted to illustrate the validity of the proposed method. Comparisons with the conventional control charting procedure are also provided. The analysis of the monthly number of drug crimes in the city of Pittsburgh is displayed to illustrate our current method of process monitoring.