4.4.1. Artificial Neural Networks

In 22 studies, ANNs were considered the primary technique. Seven of the 22, compared the ANN models with other techniques, such as MRA, CBR, and SVM. In six studies there were no comparisons, and the main objective was only to introduce ANN as an accurate technique for cost estimation. The comparisons between different ANNs were considered in nine of the publications listed in Table 5, which shows that the improvements of the models were achieved predominately by optimising the ANN architecture by different techniques or methods. Generally, Genetic Algorithms (GA) were utilised to improve the ANN architecture components. Kim et al. [52] optimised the number of neurons in the hidden layer and the learning rate of the neural network. On the other hand, Elhag and Boussabaine [48] compared two ANNs, using 13 parameters and using only four.

**Table 5.** Improvements in ANN models from studies.

