thanks everyone, I guess I only need to catch up with under math courses. I hv borrowed math books for econ under and see what I can do....... I also know there is still a long way after I finish under math courses............... thanks fzxc613, I will try to contact lixue schwuer, I will consider to take some statistics courses when I am in phd program if I could. ....
Actually it may not be that hard. Many American students in Econ PhD programs have crappy quantitative skills. Try to talk to some Econ professors. heihei.