From Table 3, we can see that the wheat acreage of 2009 is highest correlated with the mean wheat acreage of 2006, 2007, and 2008, with 2008 as the year showing the next highest correlation levels. It explains clearly, why and have similar sampling accuracy levels and why these levels are higher than those of and . However, in our proposed method (TSS), we used mean wheat acreage of 2006 to 2008 as the auxiliary variable in the second stage of stratified sampling rather than the wheat acreage of 2008 for two reasons. First, the correlation between the wheat acreage of 2009 and the mean wheat acreage of 2006 to 2008 is highest; therefore, it is expected that using the mean wheat acreage as auxiliary variable could achieve higher accuracy. Besides, in terms of relative efficiency, which is approximately , where is the correlation coefficient,10 the mean wheat acreage of multihistorical years could improve the regression estimation precision about 2.5 times. Second, it is difficult to determine which year has the highest correlation with a target year, especially for an investigated area without enough background information about planting systems. Hence, the mean wheat acreage of multihistorical years can be defined as an ideal variable for stratum division and acreage estimation, which can reduce the indeterminacy of auxiliary variable definition using only historical single-year wheat acreage data.