Drs. Mandla Diko

PhD student

Mandla Diko is our international PhD student. His research focuses on improving control charts, some background information follows below.

For decades control charts have been used as effective tools for detecting process changes that may affect the quality of products and services. Usually, the parameters of the process are unknown and are estimated from the Phase I process data before being used to construct control charts for Phase II process monitoring. Using parameter estimates to construct Phase II charts is known to degrade chart performance, for example the in-control average run-length of the chart may be shorter than nominally expected, causing higher false alarms. These effects of parameter estimation on control chart properties have been widely studied. However, the question of “how to adjust the Phase II limits to compensate for the effects of parameter estimation?” still needs further investigation.

His reserach focuses on the issue described above by numerically finding the correct charting constants of a Phase II chart with estimated limits, based on a given amount of Phase I data and a given nominal value of some control chart performance criterion. It also compares this numerical approach with other approaches such as the bootstrap method. The research is led by Professor Ronald Does and Professor Subha Chakraborti.