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The need on application of advanced technology in construction industry necessitates continuous employment of new technology workforce and acquiring of latest machinery. A construction firm would require a huge investment in order to survive in getting new jobs. Thus, very often, a construction project is managed by a general contractor, which sublet the works out to different subcontractors so that the general contractor can save on construction cost to compete in price 
Subcontractors are specialist in the execution of a specific job, they act as a agents of the production system of the contractor company in supplying materials, manpower, equipment, tools or designs . Chiang  concludes that subcontracting is essential to save construction cost of general contractors to compete on price. Teixeira & Couto  also agreed that increasing of specialisation thorugh subcontracting can assist in attaining the project objectives.
When the scope of work and logical dependencies between subcontractor works are not fully understand by general contractor and owners, it became a critical problem to the success of complex and fast-paced projects. Cost litigation and dissatisfied customers due to the conflict between general contractor, subcontractors and other project participants would then followed 
Subcontractor is a common term used in construction. Due to the uniqueness of each construction project, the work force is transient, multiple craft are involved, each projects are planned and worked in short time frames, and variety of materials and equipments required, one single construction project is often sublet to many subcontractors ,[5-12]. Subcontractors can contribute more than 50% , and can be as much as 90% of total project value to a construction process.
A construction project is awarded to a general contractor or prime contractor or principal contractor or main contractor, which resorts their work out to specialized outside firm to carry out specific project activities. General contractors are responsible for managing the project such as contract administration with clients, project financing, material and equipment procuring, and monitoring the project progress . According to Albino & Garavelli , the general contractor's perfomance are strongly dependant on subcontractors. This statement is reinforced by Mbachu  which stated that the ability of the general contractor and consultant to deliver the project within time, quality and cost depends largely on performance of subcontractors.
A subcontractor is a construction firm that contracts with a general contractor to perform some aspect of the general contractor's work. In most construction projects, a vital role is played by subcontractors who are hired to perform specific tasks on a project. In the usual case, the general contractor will perform the basic operations and subcontract the remainder to various specialty contractors. Subcontracting is used much more extensively on housing and building construction projects than on engineering and industrial projects .
Types of Subcontractors
Attempts have been meade to differentiate subcontractors. In Hong Kong, Ng et al. classified subcontractors to (i) equipment-intensive subcontractors (who are hired due to their specialized plant and equipments), and (ii) labor-intensive subcontractors (those who are hired as a result of their specialized labor resources.
Costantino et al.  revealed that labour-only subcontractor beneficial the subcontractor by reducing the cost of mobilization and purchasing material. Furthermore, it also offers economic advantages to the general contractor by avoiding the mark-up of full subcontracting. Quality problems and claims may still occur in getting the supply of material for application of this labour-only subcontractor. Therefore, some general contractors prefer full subcontracting to shift risk and liability.
Partnering relationship between general contractor and subcontractors were proposed to create a win-win situation ,. According to Lee et al. , this long-term relationship must be established to avoid adversarial relationship between general contractor and subcontractor. Several types of relationships between general contractor and subcontractor are discussed, competitive relationships and strategic relationships were among them. Comparison model based on transaction cost for both general contractor and subcontractor are developed respectively for each relationship.
Further subcontracting by subcontractor, or called multilayer subcontracting/latent subcontractor, allow the subcontractor to be less vulnerable to fluctuation in business, have more flexibility in workforce coordination, and be able to reduce cost of management.
In Turkish, practice of subcontracting work by subcontractors to secondary subcontractor is widespread . A study on 35 general contractors and 56 subcontractor organizations revealed that most of them are willing to sublet their work under overload of work or time pressure.
When "latent" subcontractor happened, the extent of subcontracting is even larger. "Latent" subcontracting, or multilayer subcontracting is the further subcontracting down the stream by subcontractors with or without the knowledge or consent of the general contractor or client. This has been alleged to be one of the major causes of poor construction quality and construction site safety in Hong Kong ,. Ekström et al.  argues that payment to the second tier subcontractor/suppliers can be part of the performance measurement when evaluating subcontractor.
Problems of Subcontracting
Ability to communicate and coordinate the work of subcontractors has been identified as one of the main conceptual determinants of construction project management competence in China .
Subcontractor failure has been listed as one of the risk allocated to general contractor in construction contracts. This is supported by El-Sayegh  which stated that subcontracting is risky and can lead to low quality, delayed completion and unsafe practice. Another risk created by subcontractor is the possibility of them to breach contract and dispute with the general contractor. Hence, subcontracting has been listed as one of the significant factors causing delay United Arab Emirates , and Malaysia,.
PERTINENT STUDIES ON SUBCONTRACTOR
Focus of researchers goes to either determining the constituents of subcontracting or developing new approaches/techniques to select and/or manage subcontractors. Subcontractor has become an issue on its own, separated from selection/management of general contractor by client/consultants due to its complexity. Numerous subcontractor selection and monitoring model has been proposed ,,[28-30].
Selection of Subcontractor
Many selection methods of subcontractors has been proposed in the literature. Arslan et al.  developed a web-based subcontractor evaluation system (WEBSES) to ease the selection of subcontractors. The criteria for evaluating was identified by estimators of construction firm in USA based on a database of approximately 4000 subcontractor firms.
Ng & Luu  developed a model for subcontractor registration decision through case-based reasoning approach. 12 experts were interviewed to provide essential steps needed for differentiating good and bad subcontractors. The model developed use each attributes' calculated ratings for identification of matching cases and similarity score of each individual cases. The historical data of subcontrators can be retrieved and use for the current evaluation. Weighting of all atributes can be easily modified according to the users preference, thus the effectiveness of this model is still very much depends on the experience and knowledge of users.
Manoharan  proposed a subcontractor selection method using Analytic Hierarchy Process (AHP) based on 29 questionnaires collected from contractors involved in construction projects located at Putrajaya, Malaysia. It is an Expert System to assist the main contractors in making their decision by using pairwise comparison. The decision maker will need to make their own judgement on the relative importance of each element with respect to the elements at a higher level. Argument might occur when the judgement of different decision makers are diverse.
As an effort to reduce the incidents of delay, and other possible problems that might be originated from the problems of selecting the wrong sub-contractor, this study aims to expand the sample of study as suggested by Manoharan in the effort of create an more reliable and applicable sub-contractor selection model.
Management of Subcontractor
Selecting the right subcontractor does not guarantee the success of a construction project. Coordination and monitoring of subcontracted work during the construction stage is essential. Ko et al.  developed a Sub-contractors Performance Evaluation Model (SPEM) by employing Evolutionary Fuzzy Neural Inference Model (EFNIM). Subcontractors were evaluated by field superintendents according to the types of subcontract. Different evaluation factors were adopted for different subcontract to achieve fair evaluation.
Albino & Garavelli  proposed a rating system for management of subcontractor by using neural network. An application case related to the evaluation of potential subcontractors competing for a bid has been used to show the practical implementation of this neural network. In accessing the competitor subcontractors, the decision maker have to consider five main parameters, namely price reduction, time reduction, technical/qualitative characteristic of the bid, contractual reliability of the competitor, and management skills of the competitor. The network will propose a suitable subcontractor based on previous decisions made by the expert. Therefore, examples of previous decisions need the expert to be inserted into this neural network.
Dainty et al.  focused on supply chain's management from the perspective of subcontractor. The role of subcontractors in UK construction industry is explored and followed by proposal of a framework for addressing current barriers to supply chain integration.
Subcontractor has become a great subject to all the practitioners in construction industry due to the common practice of subletting construction works into smaller packages in construction industry. Effective subcontractor selection and monitoring which can minimize the problem would determine the success of construction companies.
Problems of subcontractors, if ignored, can cause an immense impact to the construction project, and can extend into the operation of the general contractor's organisation. Therefore, attention shall be given to the issues of subcontractor, which is the main participant in almost all the construction projects.