Sporysz, M., M. Szczuka, S. Tabor, K. Molenda, and M. Kuboń. “The Use of Cluster Analysis in Assessing the Sustainability of Organic Farms. Part I. Methodical Considerations”. Agricultural Engineering , Vol. 23, no. 4, Dec. 2019, pp. 69-76, http://agriceng.ptir.org/index.php/AgricEng/article/view/208.