Is it possible to NOT guess on the GRE? Here's my somewhat long winded, but
hopefully informative response...
With the move to computer adaptive testing for the GRE, you can not go back
and change an answer. After each question, your score and the measurement
error is recalculated. Then based on your new score, an item of appropriate
difficulty is selected and presented. (Extremely simplified explanation:
you get a question right, then your ability estimate goes up and you get a
harder question. If you get it wrong, your ability estimate goes down and
you get an easier question.) Eventually, through the wonders of
probability, a stable ability estimate results, and you have a score.
Although I can't say for sure, I don't think you can skip a question with
the computerized GRE for the same reason. How would the program treat an
omitted item when recalculating your ability estimate? IF it does allow you
to skip a question, the program would most likely give you a question of
similar difficulty, but it couldn't give you too many questions at the same
level because of test security issues. And if you can't skip a question,
you have to guess.
If memory serves me correctly, the GRE is based on a 3 parameter model
which includes a guessing value, so the expect people to guess on some of
the items. (Actually, I think ETS uses a fixed guessing parameter for all
items, but I can't remember for sure.) And if this is the case, why does
ETS imply that it is more of a problem at the end of the test?
My (semi-educated) guess is that towards the beginning of the test, the
program is still trying to get an ability estimate by using a wider range
of difficulties. Basically, it expects to make mistakes in the estimation
of your ability and hence the questions it presents to you. Towards the
end, it is trying to reduce the measurement error by using more items of
similar difficulties. So, guessing at the start wouldn't have much of an
effect because it hasn't narrowed in on any specific estimate. Also, the
more questions you have remaining, the more you can bring up your score.
But at the end of the test, missing too many questions in a row might bring
down your estimated ability so much that you can't recover with the limited
number of items remaining. Also, it would increase the measurement error,
resulting in a more inaccurate score.
In the end, one point about guessing holds true regardless of the test or
test format: When you get the question right, guessing helps you out. When
you get the question wrong, it hurts your score.
The catch with the computerized GRE: if you don't know the answer, you have
to guess.
Hope this helps a little... and if I'm wrong on this, please let me know...
- Marc
PS- Ask me this question again in about 4-5 months after I've finished the
lit review of my dissertation on alternative scoring methods for
computerized adaptive tests, and I might be able to give a better answer.
G. Marc Turner, MEd
Lecturer & Head of Computer Operations
Department of Psychology
Southwest Texas State University
San Marcos, TX 78666
phone: (512)245-2526
email: [EMAIL PROTECTED]
