Using process modelling and simulation to decrease backlog and reduce overall throughput time

Breaking down the problem, defining the goal

The primary goal was to reduce the backlog in the process. Little’s law teaches us that the number of cases in a process (in this case the backlog) is equal to the product of the arrival rate of new cases multiplied by the average time spent in the process (L=λW). Since the arrival rate was beyond the control of the organisation, a reduction in backlog had to come from a reduction in ‘throughput time’ (TT). There was a suspicion that a significant part of the throughput time was the time taken by cases waiting to be processed (‘idle time’). Given the constraint that the team’s maximum capacity was fixed, and the reassurance of the process owner that everybody involved was an expert in their field, significant improvements in active time were unlikely to be achieved. So, the focus turned to the idle time. 

Interviews with the stakeholders indicated that planning for this process was not required: every new case needed to be processed as quickly as possible. Instructions and information to complete a step were readily available. The tool used to support the process (a spreadsheet tracker) worked well and was never the bottleneck to completing a step. Neither was capacity spillover an issue from the perspective of this process.

However, some people were concerned that they were involved in many processes at once. Sometimes there was simply too much work for them to do. This concern was voiced to management and addressed outside the scope of this project. It was agreed that focusing on awareness and on the setting of priorities would be a good way to start. This could be achieved by communicating metrics and sending reminders for cases that were nearly overdue to the people involved. Communicating these cases also facilitated the redistribution of the workload in case a capacity spillover was imminent.

The secondary goal was to reduce the number of overdue cases. However, no threshold values for maximum TT were defined internally or available externally. Communication of maximum TTs could also contribute to the prioritisation of the work and create a sense of urgency. In addition, maximum TTs provide the means to determine overdue and on-track cases, necessary for the metric’s communication and for reminders. For a threshold to be effective, the value should be ambitious but feasible. To determine the ideal values, and to assess the impact on the total backlog of the process, the process was simulated.