Comparison of multi layer perceptron (MLP) and radial basis function (RBF) for construction cost estimation: the case of Turkey

In Turkey, for the preliminary construction cost estimation, a notice, which is updated and published annu­ally by Turkish Ministry of the Environment and Urbanism, known as “unit area cost method” (UACM) is generally employed. However, it’s known that the costs obtained through this method in which only construction area is taken into consideration have significant differences from actual costs. The aim of this study is to compare the cost estimations obtained through “multi layer perceptron” (MLP) and “radial basis function” (RBF), which are commonly used artificial neural network (ANN) methods. The results of MLP and RBF were also compared with the results of UACM and the validity of UACM was interpreted. Dataobtained from 232 public construction projects, which completed between 2003 and 2011 in different regions of Turkey, were reviewed. Consequently, estimated costs obtained from RBF were found to be higher than the actual costs with a 0.28% variance, while the estimated costs obtained from MLP were higher than actual values with a 1.11% variance. The approximate costs obtained from UACM are higher than actual costs with a 28.73% variance. It was found that both ANN methods were showed better performance than the UACM but RBF was superior to MLP. First published online: 24 Aug 201

Public procurement law in Turkey

Various changes brought about by the public procurement law (PPL) in the construction procurement system of Turkey are discussed. Through the new procurement law, a public procurement authority (PPA) was founded to develop standard procurement documents, to provide training to workers in the public and private sectors, and to collect and publish statistical data related to the procurement system. Under the new law, purchasing goods, services, and the procurement procedures of the construction business are identified separately to enhance practicability. The public purchasing system in Turkey is the biggest employer in the country and must be effective in creating impartial rivalry conditions to provide better quality goods

Industry financial ratios - application of factor analysis in Turkish construction industry

WOS: 000241590600040Turkish economy has been hit by various economical crises between the years 1998 and 2001 and the economic stagnation still continues. Past experiences in various countries show that it is vitally important to encourage construction activities in order to get out of stagnation, as construction output directly affects about 200 other sectors and industry financial ratio analysis is a means to provide a basis for the governments to undertake corrective action. However, there are over 50 financial ratios that can be used during analysis and some are more important than the others for different industries. Previous research has shown that there are about 25 factors that are important for the construction companies. This, in turn, requires elimination of unrelated data. Factor analysis is a data reduction and classification technique, which can be applied in financial analysis. Factor analysis was thus applied to the financial data collected from Turkish construction companies for a 5-year period in order to determine the financial indicators that can be used to analyse the financial trend of the industry. Five independent factors, i.e. liquidity, capital structure and profitability, activity efficiency, profit margin and growth, and assets structure were identified to be sensitive to the economical changes in the country. The results of the factor-based analysis can be used both by the government to analyse the changes in the industry with respect to time and by the construction companies to analyse their financial state with respect to their rivals. (c) 2005 Elsevier Ltd. All rights reserved

Comparison of Unit Price Method and Unit Area Cost Method for Construction Cost Estimation

In the construction industry, increasing competition environment has led to decrease in the profit share of the projects. Accordingly, importance of construction cost estimation works has been increased for both the employer and the contractor. The purpose of this study has been to determine and compare the construction cost estimations obtained by widely used databases, "unit price method" (UPM) and "unit area cost method" (UACM) in Turkey. For this purpose, construction data from 420 projects, which were procured in accordance with the Public Tender Law no 4734 by the Turkish Ministry of Environment and Urbanism and completed between 2003 and 2011, were reviewed. Root mean square error (RMSE), mean absolute percentage error (MAPE) and coefficient of determination (R-2) were calculated for the comparison of actual and estimated cost values. Consequently, RMSE and MAPE values from UPM were underestimated with the ratio of 13.57% and 1.73% than UACM. Although UPM showed better performance than the UACM, it is not at a satisfactory level