Object Weighting: A New Clustering Approach to Deal with Outliers and Cluster Overlap in Computational Biology.

Considerable efforts have been made over the last decades to improve the robustness of clustering algorithms against noise features and outliers, known to be important sources of error in clustering. Outliers dominate the sum-of-the-squares calculations and generate cluster overlap, thus leading to unreliable clustering results. They can be particularly detrimental in computational biology, e.g., when determining the number of clusters in gene expression data related to cancer or when inferring phylogenetic trees and networks. While the issue of feature weighting has been studied in detail, no clustering methods using object weighting have been proposed yet. Here we describe a new general data partitioning method that includes an object-weighting step to assign higher weights to outliers and objects that cause cluster overlap. Different object weighting schemes, based on the Silhouette cluster validity index, the median and two intercluster distances, are defined. We compare our novel technique to a number of popular and efficient clustering algorithms, such as K-means, X-means, DAPC and Prediction Strength. In the presence of outliers and cluster overlap, our method largely outperforms X-means, DAPC and Prediction Strength as well as the K-means algorithm based on feature weighting.