title: A Variable Sampling Interval Synthetic Xbar Chart for the Process Mean.
abstract: The usual practice of using a control chart to monitor a process is to take samples from the process with fixed sampling interval (FSI). In this paper, a synthetic X control chart with the variable sampling interval (VSI) feature is proposed for monitoring changes in the process mean. The VSI synthetic X chart integrates the VSI X chart and the VSI conforming run length (CRL) chart. The proposed VSI synthetic X chart is evaluated using the average time to signal (ATS) criterion. The optimal charting parameters of the proposed chart are obtained by minimizing the out-of-control ATS for a desired shift. Comparisons between the VSI synthetic X chart and the existing X, synthetic X, VSI X and EWMA X charts, in terms of ATS, are made. The ATS results show that the VSI synthetic X chart outperforms the other X type charts for detecting moderate and large shifts. An illustrative example is also presented to explain the application of the VSI synthetic X chart.
authors.affiliation: School of Mathematical Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia.
authors.forename: Lei Yong
authors.initials: LY
authors.lastname: Lee
authors.affiliation: School of Mathematical Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia.
authors.forename: Michael Boon Chong
authors.initials: MB
authors.lastname: Khoo
authors.affiliation: School of Management, Universiti Sains Malaysia, 11800 Penang, Malaysia.
authors.forename: Sin Yin
authors.initials: SY
authors.lastname: Teh
authors.affiliation: School of Engineering, Computing and Science, Swinburne University of Technology (Sarawak Campus), Sarawak, Malaysia.
authors.forename: Ming Ha
authors.initials: MH
authors.lastname: Lee
mesh_terms: D008962:Models, Theoretical