What are my chances for a Stat/Biostat PhD?

[Mohamed Abbas]

I am a graduate of a top-10/15 US institution (think ivy league/Stanford/MIT), with a 3.8 CGPA (similar-ish major GPA), and I'm looking to apply to Biostatistics and Stat PhD programs for next year (2019). However, few things are a little worrying for me;

First, I minored in Stat as an undergrad, and I majored in Math/Econ, and I've been out of school for 2 years now, worked as an RA but in an economics department, where my research was pretty heavily economics. One project I worked on was more data oriented but it had to do with wages and employment and another was more of an economic tax model. None of these projects were really related to Biostatistics or even arguably Statistics in any remote way. I am currently working as a data analyst at a healthcare related company, but my role thus far does not involve anything really technical, it is rather boring and dry thus far, although through my time there I have gotten an opportunity to read through some of the research they do in the department I work in, much of which I actually find quite interesting. I have also tried to spend some time going through research biostatistics departments have done. I've found this very interesting, much more interesting than the econ research I did. However, since I haven't been directly involved in any stat or biostat related research, I feel like this will severely limit my application.

Second, my personal statement- I am trying to draft one right now, but I am having a little bit of trouble explaining the transition from economics to biostatistics/statistics, especially because my interest has been almost exclusively through my own reading and my appreciation for statistical models over economics ones. During my experience as an RA, as much as I enjoyed the data task that I worked on, I developed more and more skepticism of economic models during the time I was there, as they relied on too many assumptions which I felt were rather unrealistic. Is it a good idea to say this plainly in the personal statement? Or should I focus more on how the data task motivated me to explore the statistics avenue more, and I grew interested in healthcare more through my own research and my role in my current job, even though the stuff I am responsible for does not amount to much in the research framework.

Third, LORS/Grades- My grades are mostly pretty good, but I do have some poor ones, i got 2 B's in my soph year in Linear Algebra and Statistical Inference and I also got an A- in probability, my freshman year. The rest of my grades are good, all A's and a few A+'s (very strong upward trend, 4.0 all of junior and senior year), I have two semesters of real analysis as well, but no bio background whatsoever, apart from in high school. On the LOR front though, is it better to ask a math professor I took calculus III with (at my school calc III was actually linear algebra and diff equations) in which I got an A+ to write one letter, because that would hopefully make up for the other class which is listed as linear algebra, in which I got a B in? The material was essentially the same really, the class I got a B in however was much more computational and silly mistakes on exams cost me. Because I am currently thinking about whether to ask that professor or to ask the professor I did research with on the economic tax model I was referencing earlier. Although, the tax model did involve actual research, I am not sure how relevant it would be to a statistics or biostat department.

Fourth, GRE- I took the GRE general test, I got a pretty OK score, got 154 in verbal and 165 in quantitative. Is it worth redoing the GRE? I have heard mixed opinions and while I'm aware that the score isn't brilliant, is it going to be enough to get past the initial review? 

Given all these factors would you say I have a shot at any top 20 biostat/stat programs? I am obviously going to spread out my choices, but I'm just trying to decide how to split them across my applications.

Thanks very much for your help.