One of the questions that arises almost every time a new Kanban system comes to live is something like “But if I work on tasks in different stations (columns) then my personal WIP-limit has to be bigger than one, right?”
Let me answer this by a simple calculation:
Given the cold hard truth that multitasking actually means task-switching there is a very simple formula to calculate your effectiveness for the average task you are working on:
If n is the number of concurrent tasks, then each task is idling around (n-1)/n of the time.
If you work on one task at a time this formula yields zero. Because the task is never left neglected and you work on it all the time.
If you work on two tasks at a time, each of them is idling around 1/2 the time. On average.
If you work on three tasks at a time, each of them is idling around 2/3 of the time. On average.
If you work on eight tasks at a time, each of them is idling around 7/8 of the time. On average.
Or to put it in percentages
- 1 task: 100% active, 0% idle
- 2 tasks: 50% active, 50% idle
- 3 tasks: 33% active, 66% idle
- 8 tasks: 12,5% active, 87,5% idle
This means that a task that would take an hour on average will take 8 hours if you multitask 8 fold. On average. And that’s not even taking any costs into account for context switching!
So, yes can multitask a little, but –like magic– multitasking comes at a price. Be sure you are willing to pay it.
till next time