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Christoffer (6) [Avatar] Offline
Chapter 2.8.2
Second, you're concerned with cycle times in the aggregate, and not with the fine grained difference from one work item to the next. You don't try to include outliers in the calculations for future planning.
(Emphasis mine).

I don't fully understand the idea of not including outliers, they have to be included in the mean calculation otherwise the set of outliers and mean would be completely different. In other words all values must be included in reaching the value to be used for future planning. Can somebody please elaborate on the sentence of not including outliers for future planning?

My best assumption/guess is that instead of talking about cycle time variation between maximum and minimum cycle time (including outliers) it is only wise to talk about mean and +-1SD.

--- EDIT ---
On the same topic in Chapter 2.10.2 Throughput
Just as you did with cycle time, you discount observations that lie more than one standard deviation from the mean.

In Figure 2.51 it says "Outliers not relevant for planning". Although, they have already been included in the calculation to get the mean and +-1SD values.