|Barton and Collins (1997) distinguish four types of evidence:
Artifacts are documents produced during academic work, reproductions document their work outside regular studies, attestations are documentation generated about student's academic progress.
In fact there are only productions that are prepared specifically for portfolio. They may include: goal statesments, reflective statesments (students write on reviewing and organising the evidence from their portfolios) and captions (description of the evidence articulating what it is, why was it selected)
(Barton J., Collins A. (1997) Portfolio assessment: A Handbook for educators, cited after Barrett H. Pedagogical issues in Electronic Portfolio Implementation(2002)