Statistical, Empirical Data to Support Smaller Writing Class Sizes and Retention

I'm serving on a summer committee which has been tasked to research if and how smaller freshmen writing class sizes serve to incease retention within both the freshman writing course(s) and later composition courses. The report that we'll be presenting in September is directed at the college deans and provosts, so we need to uncover data that supports what most writing teachers know--smaller classes equals a better chance at student success, and we need to consider the issue from an institutional / financial as well as classroom/pedagogical perspective.
From my very cursory research, it seems that most research points to the need for smaller class sizes but doesn't offer specific statistical data to support a college's decision to lower class sizes. If I'm wrong about this, please correct me. If fellow members of WPA are researching this topic or know of resources that I should look at, please email me at joanna dot howard at montgomerycollege dot edu.

Thanks much.

Joanna Howard
Professor of English
Montgomery College--Rockville
Rockville, MD