Limitations Truly similar projects must exist. Methods are time- consuming. Detailed data needed may not be available, especially early in a program. Integration costs may be disregarded. Process is costly Less accurate than other methods, tends to overlook lower-level components, provides little detail.
Experts tend to be biased, and knowledge level is sometimes questionable.
They are often inaccurate and unstable. Also, calibration to historical data may not be relevant for new programs. According to NASA s Handbook, estimating by analogy is the act of comparing the proposed project to previously completed similar projects where project development information is known. Actual data from the completed projects are extrapolated to estimate the proposed project. Estimating by analogy can be done either at the system level or the component level.