CW Phd Critical Writing Sample

[spearmo]

I'm looking into applying to some PhD programs in creative writing. My MFA was in poetry a couple of years ago. 
 

I was wondering if anyone had any good suggestions for what some good example topics are for a critical writing sample. (some are looking for 10-15 pg) I haven't done much critical writing since undergrad (about 6 years ago now) and have only done some book reviews here and there. 

Also, does anyone know how much the critical writing sample matters over, the cw portfolio and aren't there programs that don't require it?

Schools I'm considering: Texas Tech. U of Cincinnati, U. of Houston, U of Missouri, W. Michigan,  U. of GA.

Any advice would help. Thanks!