CDM Substructure in Gravitational Lenses: Tests and Results
  We use a simple statistical test to show that the anomalous flux ratios observed in gravitational lenses are created by gravitational perturbations from substructure rather than propagation effects in the interstellar medium or incomplete models for the gravitational potential of the lens galaxy. We review current estimates that the substructure represents between 0.6% and 7% (90% confidence) of the lens galaxy mass, and outline future observational programs which can improve the results. 
C.S. Kochanek (1), N. Dalal (2) ((1) Center for Astrophysics, (2)   Institute for Advanced Study)