When we decrease budget in iron triangle, is it necessary that scope must decrease?



  • Say scope remains constant, then if cost decreases, time should increase.

    But if cost decreases and scope decreases then time should also decrease. Shouldn't it? Is that first figure correct? enter image description here



  • The relationship between cost, time, and scope is a bit more complex. The main statement is that you cannot tweak one corner of the triangle without affecting at least one of the others, too, but the direction isn't always obvious.

    There's a factor which has been left out of these diagrams (team size), and if you assume that is constant, then you're right that a budget cut should both decrease the possible scope and the total time to completion. That would mean that the upward arrow in the first diagram is wrong.

    The second diagram seems to assume that team size is increased to be able to manage the same scope in shorter time. Naively, this would not affect total cost (if 5 devs get the project done in 10 weeks, then 10 devs should get it done in 5 weeks at the same cost) but in practice this isn't true due to increased communication and learning overhead. However, that cannot be expressed in a single general formula (there may be approximations valid for specific areas).

    I would somewhat question the reliability of your source. Even if it's printed on paper, sometimes you need to question the truth of what you're supposed to learn. Learning material authors are humans, after all, and they do make mistakes.


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