-1.238是mean black(列(2))的6.845减去mean white(列(1))的8.083,即均值的差
括号内都是标准差(如果命令后面加上pvalues这个option的话括号内即使p值)
原文“ For each variable, the first row contains means and difference in means, while the second row contains standars deviations and standard errors (or p-values).”
详见help balancetable