def verify_equal_vector_lengths
      vector_lengths = @vectors.collect{|vector| vector.length}
      raise IndexError, "Unexpected behaviour: The vectors going into the STAPLE analysis have different lengths." unless vector_lengths.uniq.length == 1
    end
def verify_equal_vector_lengths
      vector_lengths = @vectors.collect{|vector| vector.length}
      raise IndexError, "Unexpected behaviour: The vectors going into the STAPLE analysis have different lengths." unless vector_lengths.uniq.length == 1
    end
Ensures that the number of voxels are the same for all segmentation
 vectors going into the STAPLE analysis.

 raise [IndexError] if the vectors to be compared in the STAPLE analysis are of different lengths