At Washington State University, as at many other institutions using portfolios, students are involved in selecting material that goes into their portfolio. These criteria can then be used by the class and referred to by the instructor in evaluation and portfolio assessment. Generalizations of this type, based on close reading of portfolios, can point us toward evolving writing assignments and evaluation methods appropriate to each General Education Level. Student writing assignments, preferably some with stages and drafts to give a notion of process, writing performances that address the program objectives and give you insight into curriculum. Completing such self-reflective writing can be made part of the course grade.
Portfolios produce richer, cross-sectional data.
You can't ask a lot of questions of survey data. It isn't necessary to evaluate every student's portfolio, but it is important that you ask specific questions of the portfolios you select for program assessment. At WSU we don't give much of a rationale, but more should be given. We do a self-study routinely every two years. This gives us a good idea of how much writing takes place at each stage of our program.