Estimating – Feedback Required

Paul Naybour

Explain the
prerequisites required for each of the following 3 estimating methods (30

Comparative Estimating
Bottom up / Analytical
Comparitive estimating takes a product which has already
been produced and uses its actual values as the basis for the estimate of the
new product. A typical example might be a warehouse which is 10000 square
metres and now you wish to build one which is 20000 square metres.  In order to estimate accurately you would
need (i) the actuals from the project used to build the first project (II) that
the new product is very similar to the first product, (III) that the same
suppliers are involved (IV) that the project contexts are similar.
Bottom Up / Analytical estimating works by producing a
detailed product breakdown / work breakdown structure and then the lowest level
of the work breakdown structures are then estimating and added together to
produce the estimate. In order to estimate accurately you would need to be able
to breakdown the product to a detailed level so the scope  is well understood. Without being confident
that all work has been identified important tasks may not be accounted for
within the estimate.
Parametric estimating is typically used for construction
projects in which a computer model is used to estimate the number of items
required (e.g. floor tiles). In order for the estimate to be accurate the
computer model needs to have a sufficient history of estimate/ actuals, the
sizing supplied to the model needs to be accurate, and any deviations such as
an increased number of floor pillars could affect the estimate and must be fed
into the model.
State 4 practical
problems of initial estimates for a project with a long timescale (20 Marks)
Projects with long timescales are more likely to be affected
by fluctuation in interest rates which can affect the funding arrangements for
the projects
Projects with longer timescales could mean that the
technology being used to deliver the project will change which can vary the
User requirements in longer running projects may not be fully
known or understood. Therefore it is very difficult to estimate accurately.
The legislative requirements may change (e.g environment)
which is more likely to place additional unforeseen costs on the projects
making the initial estimates inaccurate.

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