http://forums.studentdoctor.net/showthread.php?t=245803
Based on my experience from the schools I applied to, the writing component is looked upon highly. The MPH is a graduate level program and expect graduate students to know how to write a paper. I would say do not get less than a 5. 4 is average, and is frowned upon by some universities. I would suggest getting/reading the Princeton Review writing section for the GRE if you are worried about writing an essay.