Sat Sep 11, 2010 10:30 am
e3d,
what you describe, is not a question of best practice, it is a q1uestion of two completely different information perspectives. Speaking loosely, the median of twenty-eight minutes tells you about what you usually achieve and the mean of three hours tells you how much lost service time there has been. It is not an issue of one being better practice than the other. In this case the median is probably useful for your internal assessment of your staff and the mean indicates your overall service levels achieved, something your customer is most interested in.
The obvious way to deal with outlier values is to itemize them, give them their context (why they occurred; what, if anything you are doing to prevent them; etc.) and then offer, as a second figure, the mean with them excluded. I would suggest not inflicting concepts like median on your customer, unless they are very savvy about statistics, because, otherwise, they will probably feel you are trying to hide something.
It is a coincidence (or a devious devise of some long forgotten statistician) that Mean Median and Mode all start with the letter M. In my experience the acronyms MTTF and MTBF are used quite specifically for "mean time..." and not as some clever way of saying "some form of average beginning with M" and I would not recommend using the acronyms in any other way lest you cause confusion.
"Method goes far to prevent trouble in business: for it makes the task easy, hinders confusion, saves abundance of time, and instructs those that have business depending, both what to do and what to hope."
William Penn 1644-1718