I have a MS in CS with couple extra courses in statistics at graduate level. I am interested in statistical machine learning, however the research can be carried out in Statistics and Computer science department both. I was wondering if anyone has an insight on how hard it would be to get into a statistics PhD with a Masters in CS, I do have some publications and currently working as a Statistical analyst.
There are plenty of PhD Statistics programs that would want you, just because of your background. Keep in mind that their are tons of PhD Statistics programs in the USA. You can apply to 10 relatively low ranked ones, and and 10 of your choice, and see from there, for example. One thing to reiterate, ranking is just a relative number. If you graduate and are seeking a Data Scientist position, and have a M.S. In Computer Science + A PhD in Stats, your good no matter where you went.
CS (in the theoretical track) and statistics both do considerably cover the mathematics! Actually, a robust background in mathematics could drive you to pursue the statistics program and many other interdisciplinary research fields, deservedly. With due attention to the fact that you have passed a couple of related courses in master level and taking your applied research in the target field, you have a noticeable chance to be successful in this way.