  The skew-stickiness-ratio (SSR), examined in detail by Bergomi in his book,
is critically important to options traders, especially market makers. We
present a model-free expression for the SSR in terms of the characteristic
function. In the diffusion setting, it is well-known that the short-term limit
of the SSR is 2; a corollary of our results is that this limit is $H+3/2$ where
$H$ is the Hurst exponent of the volatility process. The general formula for
the SSR simplifies and becomes particularly tractable in the affine forward
variance case. We explain the qualitative behavior of the SSR with respect to
the shape of the forward variance curve, and thus also path-dependence of the
SSR.
