The Delphi mehtod
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We continue our journey exploring available cost estimations models. Previously we have looked at non-algorithmic approaches  and COSMIC. In this blog, we will discuss the Delphi method, which can be interpreted as an extension of the expert judgement approach (discussed in this post).

The Delphi method is named after the Oracle from Delphi in Greek mythology, in case you’re wondering. The idea behind this approach is relatively easy, but it can still be challenging to implement.

The Delphi method relies on experts in the field where your estimation is taking place. There is no upper limit to how many experts can take a part in this enterprise, but the minimum is (I believe) three. You start by asking each expert individually about the estimation of the project. The original Delphi method relies on the fact that experts can estimate costs and comment on the requirements anonymously.

Then the leader of the estimation process exchanges the results among experts so they can get familiar with the opinions and estimations of their peers. The leader then repeats the process asking experts to estimate the requirements again, this time considering all notes from the previous iteration. The process ends when the experts reach a consensus, or after a particular number of iterations has taken place.

As you can see, this is quite a simple method to apply. The challenge is to find the experts and cover their labour. Additionally, depending on the number of iterations, it may be time consuming to deliver the results.

I haven’t personally tried this method, but I believe it can give an accurate result. If expert judgement is considered a reasonable way to provide reliable estimation, this method definitely makes it even more reliable by giving it structure.


The Delphi method: 

  • Can deliver highly accurate results
  • Is fairly easy to use
  • Is respected as a reliable method, even though it’s not an ISO standard
  • Can be applied to many industries or problems


However, the Delphi method also:

  • Requires a number of experts in a particular field
  • Can get expensive
  • Can be time consuming
  • May not provide good results if the scope of the estimation is too big or not well defined

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