2. The method of claim 1 wherein the text variation measures include syntactic complexity, semantic difficulty, degree of academic style, and text cohesion.
2. The method of claim 1 wherein the text variation measures include syntactic complexity, semantic difficulty, degree of academic style, and text cohesion. 6. The method of claim 2 wherein text cohesion is measured using factors from the group consisting of referential cohesion, causal cohesion, connective non-causal cohesion, and thematic continuity.