function get_records($quizid, $currentgroup, $groupstudents, $allattempts)
{
global $DB;
list($qsql, $qparams) = $DB->get_in_or_equal(array_keys($this->questions), SQL_PARAMS_NAMED, 'q0000');
list($fromqa, $whereqa, $qaparams) = quiz_report_attempts_sql($quizid, $currentgroup, $groupstudents, $allattempts);
$sql = 'SELECT qs.id, ' . 'qs.question, ' . 'qa.sumgrades, ' . 'qs.grade, ' . 'qs.answer ' . 'FROM ' . '{question_sessions} qns, ' . '{question_states} qs, ' . $fromqa . ' ' . 'WHERE ' . $whereqa . 'AND qs.question ' . $qsql . ' ' . 'AND qns.attemptid = qa.uniqueid ' . 'AND qns.newgraded = qs.id';
$this->states = $DB->get_records_sql($sql, $qaparams + $qparams);
if ($this->states === false) {
print_error('errorstatisticsquestions', 'quiz_statistics');
}
}
function quiz_stats($nostudentsingroup, $quizid, $currentgroup, $groupstudents, $questions, $useallattempts)
{
global $CFG, $DB;
if (!$nostudentsingroup) {
//Calculating_MEAN_of_grades_for_all_attempts_by_students
//http://docs.moodle.org/en/Development:Quiz_item_analysis_calculations_in_practise#Calculating_MEAN_of_grades_for_all_attempts_by_students
list($fromqa, $whereqa, $qaparams) = quiz_report_attempts_sql($quizid, $currentgroup, $groupstudents);
$sql = 'SELECT (CASE WHEN attempt=1 THEN 1 ELSE 0 END) AS isfirst, COUNT(1) AS countrecs, SUM(sumgrades) AS total ' . 'FROM ' . $fromqa . 'WHERE ' . $whereqa . 'GROUP BY (attempt=1)';
if (!($attempttotals = $DB->get_records_sql($sql, $qaparams))) {
$s = 0;
$usingattemptsstring = '';
} else {
$firstattempt = $attempttotals[1];
$allattempts = new object();
$allattempts->countrecs = $firstattempt->countrecs + (isset($attempttotals[0]) ? $attempttotals[0]->countrecs : 0);
$allattempts->total = $firstattempt->total + (isset($attempttotals[0]) ? $attempttotals[0]->total : 0);
if ($useallattempts) {
$usingattempts = $allattempts;
$usingattempts->attempts = get_string('allattempts', 'quiz_statistics');
$usingattempts->sql = '';
} else {
$usingattempts = $firstattempt;
$usingattempts->attempts = get_string('firstattempts', 'quiz_statistics');
$usingattempts->sql = 'AND qa.attempt=1 ';
}
$usingattemptsstring = $usingattempts->attempts;
$s = $usingattempts->countrecs;
$sumgradesavg = $usingattempts->total / $usingattempts->countrecs;
}
} else {
$s = 0;
}
$quizstats = new object();
if ($s == 0) {
$quizstats->firstattemptscount = 0;
$quizstats->allattemptscount = 0;
} else {
$quizstats->firstattemptscount = $firstattempt->countrecs;
$quizstats->allattemptscount = $allattempts->countrecs;
$quizstats->firstattemptsavg = $firstattempt->total / $firstattempt->countrecs;
$quizstats->allattemptsavg = $allattempts->total / $allattempts->countrecs;
}
//recalculate sql again this time possibly including test for first attempt.
list($fromqa, $whereqa, $qaparams) = quiz_report_attempts_sql($quizid, $currentgroup, $groupstudents, $useallattempts);
//get the median
if ($s) {
if ($s % 2 == 0) {
//even number of attempts
$limitoffset = $s / 2 - 1;
$limit = 2;
} else {
$limitoffset = floor($s / 2);
$limit = 1;
}
$sql = 'SELECT id, sumgrades ' . 'FROM ' . $fromqa . 'WHERE ' . $whereqa . 'ORDER BY sumgrades';
if (!($mediangrades = $DB->get_records_sql_menu($sql, $qaparams, $limitoffset, $limit))) {
print_error('errormedian', 'quiz_statistics');
}
$quizstats->median = array_sum($mediangrades) / count($mediangrades);
if ($s > 1) {
//fetch sum of squared, cubed and power 4d
//differences between grades and mean grade
$mean = $usingattempts->total / $s;
$sql = "SELECT " . "SUM(POWER((qa.sumgrades - :mean1),2)) AS power2, " . "SUM(POWER((qa.sumgrades - :mean2),3)) AS power3, " . "SUM(POWER((qa.sumgrades - :mean3),4)) AS power4 " . 'FROM ' . $fromqa . 'WHERE ' . $whereqa;
$params = array('mean1' => $mean, 'mean2' => $mean, 'mean3' => $mean) + $qaparams;
if (!($powers = $DB->get_record_sql($sql, $params))) {
print_error('errorpowers', 'quiz_statistics');
}
//Standard_Deviation
//see http://docs.moodle.org/en/Development:Quiz_item_analysis_calculations_in_practise#Standard_Deviation
$quizstats->standarddeviation = sqrt($powers->power2 / ($s - 1));
//Skewness_and_Kurtosis
if ($s > 2) {
//see http://docs.moodle.org/en/Development:Quiz_item_analysis_calculations_in_practise#Skewness_and_Kurtosis
$m2 = $powers->power2 / $s;
$m3 = $powers->power3 / $s;
$m4 = $powers->power4 / $s;
$k2 = $s * $m2 / ($s - 1);
$k3 = $s * $s * $m3 / (($s - 1) * ($s - 2));
if ($k2) {
$quizstats->skewness = $k3 / pow($k2, 3 / 2);
}
}
if ($s > 3) {
$k4 = $s * $s * (($s + 1) * $m4 - 3 * ($s - 1) * $m2 * $m2) / (($s - 1) * ($s - 2) * ($s - 3));
if ($k2) {
$quizstats->kurtosis = $k4 / ($k2 * $k2);
}
}
}
}
if ($s) {
require_once "{$CFG->dirroot}/mod/quiz/report/statistics/qstats.php";
$qstats = new qstats($questions, $s, $sumgradesavg);
$qstats->get_records($quizid, $currentgroup, $groupstudents, $useallattempts);
$qstats->process_states();
$qstats->process_responses();
} else {
$qstats = false;
}
if ($s > 1) {
$p = count($qstats->questions);
//no of positions
if ($p > 1) {
if (isset($k2)) {
$quizstats->cic = 100 * $p / ($p - 1) * (1 - $qstats->sum_of_grade_variance() / $k2);
$quizstats->errorratio = 100 * sqrt(1 - $quizstats->cic / 100);
$quizstats->standarderror = $quizstats->errorratio * $quizstats->standarddeviation / 100;
}
}
}
return array($s, $usingattemptsstring, $quizstats, $qstats);
}
