TITLE:
On Efficient Monitoring of Process Dispersion using Interquartile Range
AUTHORS:
Shabbir Ahmad, Zhengyan Lin, Saddam Akber Abbasi, Muhammad Riaz
KEYWORDS:
Auxiliary Information, Bivariate Normal Distribution, Control Carts, Interquartile Range, Lower and Upper Quartiles, Power Curves.
JOURNAL NAME:
Open Journal of Applied Sciences,
Vol.2 No.4B,
January
10,
2013
ABSTRACT: The
presence of dispersion/variability in any process is understood and its careful
monitoring may furnish the performance of any process. The interquartile range
(IQR) is one of the dispersion measures based on lower and upper quartiles. For
efficient monitoring of process dispersion, we have proposed auxiliary
information based Shewhart-type IQR control charts (namely IQRr and
IQRp charts) based on ratio and product estimators of lower and
upper quartiles under bivariate normally distributed process. We have developed
the control structures of proposed charts and compared their performances with
the usual IQR chart in terms of detection ability of shift in process dispersion.
For the said purpose power curves are constructed to demonstrate the
performance of the three IQR charts under discussion in this article. We have
also provided an illustrative example to justify theory and finally closed with
concluding remarks.