  As part of large-scale assessment project at Texas Tech University, we
studied the effect of problem format on students responses to quiz questions.
The same problem was written in multiple formats and administered as a quiz in
the large introductory physics sections in both the algebra-based and
calculus-based classes. The formats included multiple-choice (MC) only, MC and
free response (FR) and FR only. Variations in the FR wording were also
explored. We examined the ability of students to both choose the correct answer
and correctly explain their reasoning and show their calculations. We also
analyzed the type of written responses the students used to support their
answers. We found that a large percentage of the students who chose the correct
answer could not support their answer with correct reasoning or calculations.
