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  • regis hattori thinks this is interesting:

For completeness—the reverse is also true. Double the number of items you work on, and the cycle time is doubled to a whopping two months. This is provided that the other conditions (way of working, item size, people on the team, and so on) remain the same.

From

Cover of Kanban in Action

Note

the problem is that not always the condition (specially "way of working") is the same...