This interactive visualization demonstrates the Stochastic Outlier Selection (SOS) applied to roll call voting data. It was first presented at the NYC Machine Learning meetup on November 21, 2013. SOS is an unsupervised outlier-selection algorithm by J.H.M. Janssens, F. Huszar, E.O. Postma, and H.J. van den Herik (2012). It employs the concept of affinity to quantify the relationship between data points and subsequently computes an outlier probability for each data point. Intuitively, a data point is selected as an outlier when the other data points have insufficient affinity with it.
The data set contains 103 data points (senators) and 172 features (votes). The dissimilarity between the data points is the Euclidean distance. Each circle in the scatter plot represents a senator, of which the location is determined by applying the non-linear dimensionality reduction technique [t-SNE](http://homepage.tudelf