Estimate employee overhead due to interruptions

I am trying to estimate an overhead due to the effect of interruptions on an employee.

For example: Imagine an employee who is responsible for repair services. He gets called on a daily basis by external people who have questions, like to get advice etc. In addition the employee now and then gets called to help out in meeting preparations etc. All these "side tasks" appear as interruptions since they are not the employees main task but there is no one to do them other than him.

Now I am looking for studies that have researched the effect of such interruptions on the effectivity and efficiency of work. The goal is to get a percentage value of the time he is spending on their core tasks to estimate the interruption effect in hours. The result should look something like this:

Time for core task: 100 h Interruption Overhead: 10 % Interruption time: 10 h

The idea is to estimate if interruption is acceptable for a given workload or needs to be reduced by means that depend on the given situation.

• I can't help with a list of studies, per your question, but I do remember from when I was managing a similar situation I allowed 15 minutes on each "side" of the interruption to allow for the damaging effects of context-switching. In other words it's not just the time spent on the interruption, it's all the time spent switching gears in your head, putting one task aside in a tidy way and bringing another task to the fore. Generally people ignore this overheard, but the smaller the interruption the greater then context-switch impact as the 15 mins remained constant – Marv Mills Mar 4 '14 at 10:13
• That is a very interesting aspect. However, the problem with this is that it needs at least a count of interruption per time interval. The situation I am facing are employees, that should get their work done only be the time it should take them but that are complaining about constant interruptions and task switching. – fr3d-5 Mar 4 '14 at 10:18
• Well only they can measure that actual impact surely. I would be asking them to record the durations and nature of all interruptions- "You can't manage what you don't measure" – Marv Mills Mar 4 '14 at 11:07
• This question is not an exact duplicate, but the gist of the question (and the currently accepted answer) are pretty much the same as this related question. – Todd A. Jacobs Mar 4 '14 at 13:23
• Thanks CodeGnome, I wasn't aware of that. In fact, the cited answer contains exactly what I was looking for: 40 % of productive time, as cited from here. Although this is a maximum percentage there is now an upper boundary. – fr3d-5 Mar 4 '14 at 13:32

TL;DR

The results from cognitive research are largely statistical. You will not find a single canonical source for your question that can be expressed as a fixed percentage and that will be accurate across all domains.

There are, however, some generally-accepted rules of thumb for task switching, interrupted flow, and operational overhead. Each of these items is lightly touched on in the sections below in order to provide you with a starting point for your own research.

Interruptions are a form of task switching. The American Psychological Association says:

[S]hifting between tasks can cost as much as 40 percent of someone's productive time.

In other words, the more task-switching someone needs to do, the less they will get done. It's a direct hit to productivity, although the precise amount of the reduction may vary by person or situation.

Cost of Interrupted Flow

Keep in mind that interruption overhead isn't just the amount of time someone is being actively interrupted. It also includes the amount of time necessary to resume flow, and to recoup any cognitive framework and working memory they were using for the task.

This related question on Programmers Stack Exchange quotes from Peopleware: Productive Projects and Teams which posits a minimum of 15 minutes (in addition to the actual time spent on the interruption) to resume flow, but it's important to note that this is stated as a minimum, rather than as an average or a maximum. In practice, that means an interruption at a critical moment could potentially result in the entire rest of the day being wasted due to interruptions in flow, but your personal mileage will certainly vary greatly in this regard.

You want to calculate Overall Labor Effectiveness. Here is a document that discusses it:

I hate to send you to Wikipedia but this write-up shows an example of how to calculate based on what appears to be a manufacturing job:

http://en.wikipedia.org/wiki/Overall_Labor_Effectiveness

The overall OLE score will show you the employee utilization for the job you are measuring because it will reduce the availability metric. So availability for this guy's case will be reduced by all the time he gets called away for other productive work but ALSO normal, unscheduled downtime that we all have in a given 8-hour day.

Then, I think you can the OLE metric to your employee costs allowing a decent estimate for overhead interruptions but it may include, too, downtime.

Hope this helps.

I have worked both in Waterfall setting as well as Agile. From time to time it is proven that resources cannot be productive at their work for 6-6.5 hrs a day. Remaining time goes into status meeting, collaboration and 'other stuff' that deviates them from being productive.

I would agree with above suggestions that task switching is not a good idea at all. I would let the resources focus and get things done one at a time and know with decent certainty when they would get done, rather than start 10 tasks and not knowing when they might be done with them.

HTH

• I'm not sure this answers the question. OP asked for a methodology to estimate impact. You've merely agreed to his underlying assumptions. – MCW Mar 4 '14 at 16:43
• Exactly. The question aims to identify an estimate (or maybe guesstimate) when it would be useful to consider outsourcing interruptive activities such as answering the telephone or collecting data to another person (e.g. an assistant). – fr3d-5 Mar 4 '14 at 17:16
• I understand. My intention to say (from my experience) is that there is typically a waste of 15% (read interruptions) which is proven to be a practical % for our projects (which is what I wanted to mention rather than pulling out an arbitrary number). – Bobby Fisher Mar 4 '14 at 20:50
• Thank you very much. I was assuming that 10 % would be a useful first guess given that mentioned article says 40 % is the maximum. Your 15 % pretty much agrees to that. – fr3d-5 Mar 5 '14 at 10:43