# COV

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• #54071

I have a series of ( hours required )data as capacity required for a processing unit on half hourly interval . My manager wants me to understand what is the capacity they should staff at . As i understand it should include mean & measure of variation . So if the average required is 15 hrs capacity required . Do I need need to add average + COV to get the result.

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#193387

Robert Butler
Participant

I think you will have to provide some more details before anyone can offer much in the way of advice.

Questions:

1. When you say you have a series of hours as capacity required for a processing unit what exactly does this mean? My guess is that you are saying that you have some measure of time it takes X number of people to do something but it could mean any number of things.

2. If this is a situation where you need X number of people working some given percentage of their daily time to put in the 15 person hours needed to meet some kind of target then you will need to give us some understanding with respect to time/person allocation and how it is driven. If it is something else then you will need to provide additional information.

3. If we ignore all of the above and just focus on a question of time estimation then the short answer to that is – yes , you need a target and a tolerance. The tolerance is usually some multiple of the standard deviation of the process. I suppose you could use the COV but I must admit I’ve never seen anyone do this and I don’t understand why one would use the COV in this manner.

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#193421

MBBinWI
Participant

Tom: You should look at the questions from Robert. I’m going to take a guess and assume that your data is man-hours required for a task. If that is the case, you can plot these times and develop a distribution of times. Now, the question needs to be asked of your supervisor – “What percent of the distribution do you want to protect yourself against – so that you always have sufficient staff to handle the expected task?”
If we assume that your times are normally distributed, then if you set the staffing at the mean level, you will be overstaffed 50% of the time and shortstaffed 50% of the time. If you want to be able to handle up to 95% of all required times, you would staff at a level that is approx 2 std dev’s to the right of the mean. This will have you understaffed only about 5% of the time, but will be overstaffed nearly all the time.

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