Slubfurter Mental Map Survey 2000 - 2002: Nearest Neighbor Hierarchical Clustering - First Order; For each identified cluster a Standard Deviational Ellipse is calculated. Typically, one standard deviation will cover more than 50% of the cases, one and a half standard deviations will cover more than 90% of the cases, and two standard deviations will cover more than 99% of the cases, although the exact percentage will depend on the distribution (Levine, 2002).