A statistical analysis of the twinning behavior in a basal-textured Mg sheet under hard orientation loading was performed at strain rates of 1×10^-5 and 1×10^-1 s^-1 with grain sizes of 70 and 20 μm. There were 1609 tension twins identified including adequate (51%) anomalous twins (Schmid factor m<0). Twin variant selection exhibited almost no grain size or strain rate effects. Most twin variants (74%) correlated well with the proposed normalized Schmid factor (m_nor). The Luster-Morris parameter (m′) values failed to correlate with the twin transmission, while 96% of transmitted pairs exhibited large m_nor or normalized m′ (m′_nor) values. Twin transmission occurred more frequently at lower grain boundary misorientation angles (10°-30°). The active anomalous twins correlated well with m of the prismatic slip. The present work provided a statistical perspective that, the m_nor and m′_nor can correlate the anomalous twinning rather than m and m′. The local condition also played a critical role in anomalous twinning behavior.