  We explore whether the human ratings of open ended responses can be explained
with non-content related features, and if such effects vary across different
mathematics-related items. When scoring is rigorously defined and rooted in a
measurement framework, educators intend that the features of a response which
are indicative of the respondent's level of ability are contributing to scores.
However, we find that features such as response length, a grammar score of the
response, and a metric relating to key phrase frequency are significant
predictors for response ratings. Although our findings are not causally
conclusive, they may propel us to be more critical of he way in which we assess
open ended responses, especially in high stakes scenarios. Educators take great
care to provide unbiased, consistent ratings, but it may be that extraneous
features unrelated to those which were intended to be rated are being
evaluated.
