Chris Croft's Personal Blog

February 23, 2010

SPI and CPI

Filed under: Project Management — chriscroft @ 1:50 pm

Am I the only person who thinks that the definition of Schedule Performance Index shouldn’t be the value of what you’ve done divided by the value of what you should have done (google and check any website to see that this is what we are always told), but should be How long it’s taken you divided by how long you thought it was going to take you?

In other words, if you’ve done part one, woth £1000, but not done part two, worth £3000, the conventional wisdom is that you are a quarter of the way there. But if both tasks were going to take you a week each (maybe the second one jsut involved more people), then surely you are only a week behind, or half way through.

This distinction is very important because SPI is used to calculate when we are going to finish, by multiplying the length of the whole job by the SPI, so in my example above the SPI slaves would multiply the whole thing by 4, whereas I would rather multiply it by 2 (we’ve done week instead of 2 so far)

… or did I miss something?

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