OK, and apologies if you think I am bullying you (but trust me - I do know about statistics), but consider the following two return streams:
+1, +1, +1, +1, -1, -1, -1, -1
+1, -1, +1, -1, +1, -1, +1, -1
Both will have the same Z score, but the first has positive autocorrelation (positive...