Your quiz results will produce many quiz and question statistics. This page describes the meanings of those statistics.
To access the statistics for your quiz, navigate to the quiz in your course site.
Under the Administration block, select Results and then Statistics.
Attempts - number of students who have attempted the question.
Facility index - the percentage of students that answered the question correctly.
Standard deviation - the variation in the scores for the question.
Random guess score - the score the student would get by guessing randomly.
Intended weight is simply what you set up when editing the quiz. If question 1 is worth 3 marks out of a total of 10 for the quiz, the intended weight is 30%. The effective weight is an attempt to estimate, from the results, how much of the actual variation was due to this question. So, ideally the effective weights should be close to the intended weights.
This is the correlation between the score for this question and the score for the whole quiz. That is, for a good question, you hope that the students who score highly on this question are the same students who score highly on the whole quiz. Higher numbers are better.
Another measure that is similar to the Discrimination index.