Necessary and sufficient conditions for consistency of A method for smoothed functional inverse regression

Ferré and Yao (2005, 2007) proposed a method to estimate the Effective Dimension Reduction space in functional sliced inverse regression. Their approach did not require the inversion of the variance-covariance operator of the explanatory variables, and it allowed them to get √n consistent estimators in the functional case. In those papers there is a mistake. In this note we show that, in general, the approach does not give an estimator of the SIR subspace. We also give necessary and sufficient conditions for this to be true.