The stock 1.5.2 does not allow negative scores for individual questions or entire quizzes. In other words, it is impossible to use SAT or GRE style point assignments, in which a wrong answer is worth -0.25 points.
A fix is proposed as follows (for 1.5.2):
change line 864 of mod/quiz/locallib.php from
0.0), 1.0) * $question->maxgrade;
1.0), 1.0) * $question>maxgrade;