public static QuizStatistic getQuizStatistic(int QuizId)
    {
        try
        {
        QuizStatistic qs = new QuizStatistic();
        String statement = String.format("select distinct userid from quizresult where quizid = %d", QuizId);
        ResultSet rs = getQueryResults(statement);
        while (rs.next())
        {
            qs.quizResults.add(getQuizResult(QuizId, rs.getInt("USERID")));
        }
        qs.populateQuestionStats();
        return qs;
        }
        catch (SQLException xe)
        {
            return null;
        }
    }