请哪位高人帮我看看，不太明白下面这段话的红色部分。

First, as discussed above, the literature suggests a number of possible problems with the Grubel-Lloyd measure. The most important was the need for the logistic transformation of the basic measure. However various authors have considered adjustments for the ‘overall’ trade balance. This function as a ‘macro-economic’ factor at the country level and the adjusted measures are intended to reflect an overall balance of payments structure which is out of equilibrium. A country with a negative (or positive) overall trade balance for example will bias the Grubel-Lloyd index downward.

Grubel-Lloyd index, overall balance of payments 是什么关系？谢谢。