今天在看一篇名为the evolution of brand preferences的文章的时候，看到一句，
we show that this share varies significantly across space, with a mean of 0.63 and a  cross-state standard deviation of 0.15 in the average product category.
请问cross-state standard deviation是什么类型的标准差？
average product category又该如何理解？
小弟初来乍到，对经济理论的皮毛尚且不知，还望各位多多指教。谢谢。