Education research: "guessing/don't know" clicker response

Comment was made on the previous post: Astronomy clicker question: type II supernova energy source.

Thank you for providing such an extraordinary resource through your blog of questions, etc!

Question: Do you or other professors ever use (or have you considered using) a response of "? - I don't want to guess."

I used this response frequently for formative assessment questions when I taught math at the college level and integrated the use of clickers in my teaching. Students were quite willing to choose this response because they weren't embarrassed after choosing it.

By providing this response for questions used in formative assessment I was able to get better data to inform my instruction. Sometimes (much to my chagrin) 30-50% of my students would choose this response following instruction on a topic so that I then knew I should reteach the topic and then reassess.

Your thoughts on this?

Thanks.

Tim Fahlberg

Though not an option on this semester's (Spring 2008) Astronomy 10 clicker questions, there is an "I'm lost, and I don't know how to answer this" response on Physics 5A clicker questions (cf. previous post, Physics clicker question: average versus instantaneous velocity for an example), which is a much more common response by students earlier in the semester, than later in the semester, most likely due to an unfamiliarity with both clickers and the material in general. (Whenever the "I'm lost" category does become the majority of responses in sporadic cases, then yes, the instructor is obliged to diagnose the cause of the disconnect, and recover using more exposition/examples.)

Also for some clicker questions in Physics 5A, students enter a numerical value for their answer following a calculation. If students are lost and don't know how to answer the question, they are instructed to enter a "nonsense" numerical answer (e.g., "-999") rather than an approximate guess. These answers will then fall outside the correct answer (which can be extended to within a +/- uncertainty), and also amuses the class as to the creativity of "wild" answers.