我刚接触结构方程模型及AMOS，所以想请教几个问题：首先，数据需要标准化处理吗？投入产出的标准化处理方法是否一样？其次，出现This message indicates that some variance estimates are negative, or that some exogenous variables have an estimated covariance matrix that is not positive definite. It suggests either that your model is wrong or that the sample is too small 这种情况该怎么办，我的样本是217，这个样本不算小吧？请高手指点，谢谢