如何理解that is

老师，你好，想请教你一个问题
Research has found that IQ predicted leadership skills when the tests were given under low stress conditions，but under high stress conditions，IQ was negatively correlated with leadership—that is, it predicted the opposite.这个句子中的that is如何理解，前面句的IQ与领导能力呈负有关这个意思判断不出IQ预测的是相反的啊，如何会有that is（也就是说）这个短语在中间呢，麻烦老师解答一下，谢谢

Research has found that IQ predicted leadership skills when the tests were given under low stress conditions，but under high stress conditions，IQ was negatively correlated with leadership—that is, it predicted the opposite.

研究发现，在重压小的状况下，IQ可以预测领导能力；但在重压大的状况下，IQ与领导能力呈负有关，也就是说，它预测的结果正好相反。

插入成分 that is，用于引导讲解前文的意思，非常正确的。

含义是：在要紧关头，IQ高的人反而没领导能力了。