Thanks for your suggestion,
I listed as above just based on some advices from peers, my professor at Yale told me that a master did not guarantee a PhD and it was really competitive in the program nowadays. I put Michigan in realistic just because I received their master offer a year ago and it seems they accept more PhD students by looking at their website. Though I got the master offer from Brown as well, but since it was really small and has a relatively small biostats department and I am afraid it will be hard for me to get in. I heard from others that UCLA was really good and also the location is good thus making it more competitive (good in Stats as well). I really don't know whether OSU or BU or USC are harder to get in than Pitts or Iowa。。。 I ranked in this way just due to their overall ranking and reputation
Quoted : "Pick your favorite 4-6 from among: UNC, Michigan, Minnesota, Berkeley, Columbia, Penn, Yale, Brown, UCLA, Emory"
Thanks so much for your advice and your encouragement as well, I will definitely try out those.