# How to calculate the weighted average of duration or time

1. ## How to calculate the weighted average of duration or time

I've read dozens of examples of how to calculated weighted averages on cost and percentages but none had discussed time or duration as in the example of finding the average duration (in seconds) it takes some process to execute.

For example if I execute a process 10 times and in that 10 times it completes in 300 seconds the first time, then completes in 1 second on the 2nd and 3rd execution and the final 7 executions each complete in 10 seconds then the numerical average duration for these values is 37.2 seconds. Since all but 1 of the 10 executions completed in 10 seconds or less I know that the weighted average would give me more accurate value of how long on average the process will take to complete. But how do I calculate the weighted average of this process?

 #Executions Duration (secs) Total Secs Numerical Avg 1 300 300 37.2 2 1 2 7 10 70 10 372

2. ## Re: How to calculate the weighted average of duration or time

You probably don't mean weighted average.

When I do calculations like yours, I usually throw out 'outlier' values. It is both art and science to determine what an 'outlier' value is. With a small sample like yours, I would calculate the standard deviation of the values, and would throw out any value that has less than a 95% chance of not being a good value (Average +/ 1.96 standard deviations).
See https://en.wikipedia.org/wiki/68%E2%...80%9399.7_rule

This isn't really an Excel, or a statistics question, but really a process problem. The real question is why does the time to complete your process vary so much?

I hope this helps.

Lewis

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