Weaknesses

• CERs are sometimes too simplistic to forecast costs. Generally, if one has detailed information, the detail may be reliably used for estimates. If available, another estimating approach may be selected rather than a CER.
• Problems with the database may mean that a particular CER should not be used. While the analyst developing a CER should validate that CER, it is the responsibility of any user to validate the CER by reviewing the source documentation. Read what the CER is supposed to estimate, what data were used to build that CER, how old the data are, how they were normalized, etc. Never use a cost model without reviewing its source documentation.

Now that we know what a CER is, how to develop a CER, when to use a CER, and some of a CERs strengths and weaknesses, we can develop techniques for building CERs. The LSBF technique is only one mathematical transformation of the database - the linear regression model. Other sophisticated curvilinear models can also be developed, but will not be explored in this Handbook. An analyst should be mindful that little in the estimating world is linear.