各位朋友好，
        我在做一个量表的信度分析时，遇到一个问题，请朋友们指点迷津。
   问题是：在分析结果中出现了

Warnings

The determinant of the covariance matrix is zero or approximately zero. Statistics based on its inverse matrix cannot be computed and they are displayed as system missing values.

在Item-Total Statistics表格中，Squared Multiple Correlation栏为空白。请问是什么原因，我该怎么办？