What’s the difference between a cycle time and a lead time?

TimerPeople can be very definite about Lean. There are some things about which it is difficult to argue – definitions of value, waste, and takt time, for example tend to be very similar. Other terms are used in different ways by different authors, and this can be confusing. I’m not sure it matters a great deal exactly what word or phrase you use to describe a concept, as long as you are consistent about it, and can explain it clearly. Shigeo Shingo, for example, distinguishes between flow, processes and operations. I have seen ‘operations’ used as a term by Lean health care authors, but not commonly, probably because of the obvious possibility for confusion with surgical procedures.

As many of the early technical books on Lean were written in Japanese, and I don’t speak or read Japanese, I need to rely on translators to understand what was being said. The same authors can appear to be saying slightly different things in consecutive books. In some cases, they probably did change their mind, but in other instances, I suspect that it is due to translators taking similar words and translating them in to English in slightly different ways. The definitions below are examples of how I use the terms – but you will find variants. It doesn’t mean that I’m right and they are wrong – you will probably find, however, that there are different terms for very similar concepts. In using Lead time, I first decide the scope of the value stream at which I am looking. So, for example, if you take a patient going to their General Practitioner because of a symptom that is bothering them, that needs hospital referral, investigation and can then be treated with a medicine, the steps could be:

  1. Booking GP appointment
  2. Seen by GP
  3. Referral to specialist
  4. Booking process for specialist appointment
  5. Specialist appointment
  6. Attendance for tests
  7. Booking for further appointment with the specialist
  8. Second appointment
  9. Prescription taken to pharmacy
  10. Prescription dispensed

All of these steps could be further sub-divided: for example, the ‘attendance for tests’ stage requires the test to be requested, an appointment to be booked, the patient to told of the appointment, and to attend, the test to be conducted, results analysed, results returned to specialist, and so on. How specific you need to be on steps will depend on the intended purpose of the work. Lead time, as I use it, is the time from the start of the value stream until the completion of the actions for the patient. Depending on the area of improvement work, this could be the time of telephone call to book a GP appointment (step one above), to the final collection of a prescription (step 10). If, however, the work was intended to look at first attendance at a clinic, then the lead time could be from the telephone call to the General Practice to completion of the first out-patient appointment (step 5) – it will depend on the area of focus of the work. So, lead time can be minutes, days, weeks or months, depending on the area of focus. In general, I turn lead times in to minutes or seconds to give a consistent currency across all the measures that will be used, but the range of  lead times in different improvement work can be enormous.

Turning to cycle time, I use cycle time for the individual stages of a process. So, in this example, the booking process for the specialist appointment would be a cycle with a measured time. Again, the resolution can vary by project. For example, in one piece of improvement work you may be supporting a service to look in detail at their booking process: in that case, it will break down in to smaller processes, often done by different people, each of which will have a cycle time. In an overall process such as that described above, much of the waste is likely to be in the waits between cycles, so it may not be necessary to look in detail within processes, at least not at first.

Cycle times will often be very much smaller than lead times. For example, in one recent process examined, the average wait to start treatment was 214 days, but the sum of the cycle times – the time taken for all of the processes that lead up to treatment starting – was about three and a half hours. There was definite waste within individual processes – at least half an hour and probably more – but by far the largest waste was the waiting time between the cycles. You can then use your measurements to identify value to the patient by working out the value added time as a proportion of the total lead time. All of the waiting between cycles was of no value to the patient, and some of the work within cycles was also of no value. When worked out as a percentage, about 0.05% of the lead time was of value to the patient. So, I use lead time for the total length of the process of interest, and cycle time for the length of individual activities – what Shigeo Shingo would have called operations. The degree to which I break down these operations in to smaller stages would depend on the improvement work on which I was engaged.

Illustration Courtesy of Digitalart at freedigitalphotos.net

3 thoughts on “What’s the difference between a cycle time and a lead time?

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