  A new method for estimating Sobol' indices is proposed. The new method makes
use of 3 independent input vectors rather than the usual 2. It attains much
greater accuracy on problems where the target Sobol' index is small, even
outperforming some oracles which adjust using the true but unknown mean of the
function. When the target Sobol' index is quite large, the oracles do better
than the new method.
