Measurement of sustainable development, which can be realised in three aspects: economic, social and environmental, is a determinant of its efficient monitoring and implementation in various levels of management. The three orders create an integrated sustainable order. The phenomena in the individual spheres of development cannot be measured directly, however, their relationships being of a complex character. One of the methods used to identify the structure of those relationships is Structural Equation Modelling. The paper presents the results of research into the causal structure of the three spheres comprising the integrated sustainable development on the level of regions in Poland. To achieve this aim, Structural Equation Modelling and soft modelling (Partial Least Squares) were applied. Comparative analysis and evaluation of those methods was carried out in respect of their applicability, ways and methods of estimation, verification tools and requirements as to the minimum size of the sample. The research was based on a sample, defined both in time and space, consisting of 16 provinces in the years 1998-2005. Indicators of sustainable development within individual orders were used as variables. The results have proved the usefulness of the analysed methods to the verification of the basic hypothesis about relevance of social and environmental factors to shaping economic competitiveness of regions and their potential for sustainable development.