Should I become first author of a paper for which I did the statistical analysis? I am a statistician working at a research institute. We work with data from patients with a certain disease. I am getting paid by the institute, but a part of the money comes from a research grant a doctor brought in. The doctor does not work at the registry, but at a hospital and is working closely together with statisticians of the institute (including me) on research questions. 

Together we are doing research on a project. I am doing 100% of the statistics, but all the research questions and ideas come from the doctor. She is also the one writing a manuscript for a paper currently. 

Now she wants to put me as first author and herself as last author (as supervisor). The idea comes from other researchers who do something similar, but they usually have medical PhD students and not statisticians as first authors. So basically the reason she wants to put me as first author is to put herself as last author. 

I feel uncomfortable being first author and would prefer being second author. I am probably the one putting the most hours into the project by preparing all the data, doing the statistics and explaining the results to the doctor. The statistical analysis will be a big part of the paper.  But the research question is not my idea, I have no medical background, the doctor is writing the paper. I am basically getting paid to do the analysis. While I think it is interesting research, I do not identify with it and I do not agree fully with all the conclusions. So far I worked under the assumption to become co-author and the idea of making me first author came up recently. 
My opinion is that I should only be first author of my own research, which would be in statistics, not medicine.  

I guess it is very odd to reject being a first author =). 

My next step will be to talk to her about it, but I was hoping for some perspective or opinions from the community. Is it harsh/unusual to insist on being co-author only? 

Who would you suggest should be first author in this case?
In medicine, as in most biological fields that I know of, the first author is the person who did most of the hands-on work, while the last author is the one who had the idea and planned the project.  From what you've said, then, it would be appropriate for you to be first author and the doctor to be last.

That said, if you don't feel comfortable being first author (and especially in light of your comment that I do not agree fully with all the conclusions) it's also appropriate for you to request to not be first author -- some middle position (second author, or whatever) is also perfectly suitable for your contributions, from the sound of it.