* Specific program: Different graduate programs within the University of Michigan (e.g., engineering, law, business, public health) will have drastically different average GRE scores. Highly competitive programs will have much higher averages than less competitive ones.
* Year: Averages fluctuate slightly from year to year.
To find the average GRE score, you need to specify the particular graduate program you're interested in at the University of Michigan and then look for that program's admissions data, often found on the program's website. Many programs will provide this information (though not all do). You may also find unofficial averages discussed on forums like GradCafe. Keep in mind that these unofficial averages are still estimates.