The TOEFL iBT Writing Section and GRE Analytical Writing measures are intended to measure different sets of skills.
The TOEFL iBT Writing section contains two writing tasks: an independent task asks test takers to support an opinion in writing, and an integrated task that asks test takers to write responses that integrate and organize information from a reading passage and a lecture. These writing tasks are not designed to measure higher levels of critical thinking and analytical writing, but center instead on candidates' composition skills and command of English vocabulary, grammar, spelling, and syntax with some analysis and synthesis of material. Therefore, scores on the two tests are not comparable.
Because the TOEFL® test emphasizes fundamental writing and comprehension skills, the TOEFL score can supplement an Analytical Writing score by helping faculty determine whether a low score on the GRE Analytical Writing measure is due to lack of familiarity with English or lack of ability to produce and analyze logical arguments.