## 4 Discussion of the Obtained Results
This model is based on operations studies, it takes into consideration the use of linear and non-linear programming, and it offers many possibilities with respect to modelling decision problems. Model III was as just popular as Model V (5 cases). Model III enables the user to carefully prepare and conduct the entire decision-making process. By going through 11 stages, one is able to prepare input data more accurately and to verify the outcome. This model was applied in various situations, but its implementation was associated with an assessment of different variant solutions. Model II, which was used in three of the analysed cases, is similar in principle but less expanded. It was used only when making a decision to change the company's business profile. No verification of the model was noticed in any of the three cases. Model IV, close in its philosophy to model II, appeared only once, when analysing a possibility of broadening the offer, and it was not verified either. Noteworthy is the fact that the cybernetic model was not used at all. The research reported in this article showed that the most popular decision support methods employed in the construction industry when making an assessment of variant solutions are multi-criteria analytical methods and models which make use of such analyses. The study comprised problems of making decisions while performing small, medium-sized and large construction projects, characterised by different degrees of complexity. It was found that decision support models were somehow modified by users and the modifications depended on the nature of a construction project. The interviews and analyses of all studied cases enabled us to elaborate and suggest decision support models dedicated to the construction sector, including such aspects as the size of a construction project and its complexity. Suggested decision support models useful when selecting variant solutions in the construction sector:  
1. A model useful for small and medium-sized, less complicated construction projects:  
1. Study the decision situation
2. Define the problem
3. Determine criteria applied to assess solutions to the problem
4. Develop variant solutions to the problem Select a method to assess the solutions
* Assess and select the best solution
* Implement the solution
* A model for medium-sized and large, complicated construction projects: 1. Analyse the environment and collect information
* Define the problem causing difficulties
* Determine criteria for the assessment of solutions to the problem
* Develop variant solutions
* Select a method for making an assessment of the possible solutions
* Assess all variant solutions and select one
* Make a decision
* Implement the decision
* Obtain feedback
* Correct the input data, underlying assumptions  
Making strategic decisions is most often supported by models III and V. When a decision to be made concerns the future of a company, the most important stage was to collect a complete set of information about the environment (model III), as well as being able to describe the decision situation using a mathematical language (model V) and obtaining feedback which allows the user to verify the model, and in consequence to improve the decision-making process. Our suggestion of a decision support model for strategic decisions, based on this research and on experiences gained by building companies looks as follows:  
1. Identifying the need to make a decision (define the aim). 2. Collecting information about the environment. 3. Building a model (in some cases, describing the situation with a mathematical language). 4. Generating solutions to the decision problem. 5. Making an evaluation of the variant solutions. 6. Verifying the model. 7. Obtaining feedback to correct the model. 8. Receiving the corrected solution. 9. Implementation. The models designed on the basis of this study take into account the specific nature of civil engineering practice.