  Test takers do not give equally reliable responses. They take different
responding strategies and they do not make the same effort to solve the problem
and answer the question correctly. The consequences of differential test
takers' behavior are numerous: the test item parameters could be biased, there
might emerge differential item functioning for certain subgroups, estimation of
test taker's ability might have greater error, etc. All the consequences are
becoming more prominent at low-stakes tests where test takers' motivation is
additionally decreased. We had analyzed a computer based test in Physics and
tried to find and describe relationship between the item response time and the
item response likelihood. We have found that magnitude of such relationship
depends on the item difficulty parameter. We have also noticed that boys, who
respond faster, in average, give responses with greater likelihood than the
boys who respond slower. The same trend was not detected for girls.
