“…Many methods of estimating such a conditional expectation have been proposed, including kernel regression, orthogonal series estimation, nearest-neighbor estimation, and splines; see, e.g., Fan and Gijbels (1990), Härdle (1990), andSimonoff (1996) for general discussions of nonparametric regression and Haley (2014) for an application of smoothing to finance. Although, in principle, any of these methods could be used, here we use smoothing spline estimates, which are known to perform well when estimating the derivative of a regression function (Wahba 1990).…”