Two-Period Variance Ratio of an AR(1)

Returns are generated by a stationary AR(1) with autoregressive coefficient 0.5. The Lo-MacKinlay variance ratio at lag 2 is VR(2) = Var(r_t + r_(t+1)) / (2 Var(r_t)). Compute VR(2) and state whether it signals momentum or mean reversion.