Rough time for the reciprocal effects crowd: Cross-lagged panel models can’t reliably establish cross-lagged effects. Need big N, need time invariant effects, & equivalent models can't distinguish whether they exist. from Bengt Muthén & Tihomir Asparouhov www.statmodel.com/download/Rec...

Lots of difficulties yeah, but it's at least lucky that lag 0 direct effects are incoherent, except perhaps to quantum physicists :) (yes this is discussed a little in the paper).