A Detailed Comparison of Different Times Between Events Charts in Terms of the Conditional Expected Delay

ABSTRACT To evaluate the performance of exponentially weighted moving average (EWMA), cumulative sum (CUSUM) and Shewhart charts for monitoring the time between events (TBE), the conditional expected delay (CED) indicator is applied in this paper as a new metric. The Monte Carlo simulation is performed to obtain the CED profiles, which are plotted for different parameter settings. Under different upward or downward change sizes, a detailed comparison is conducted among these TBE charts. The results show that both EWMA TBE and CUSUM TBE charts outperform the Shewhart TBE chart in terms of the CED profiles under both small and large changes. Moreover, both the EWMA and CUSUM TBE charts have their own strengths and weaknesses under certain specific changes and a guide on selecting EWMA or CUSUM TBE chart based on the change sizes is provided. Finally, a real dataset of organic light‐emitting diodes (OLEDs) failure time from Samsung company is applied to show the feasibility of the CED indicator in monitoring the process.