public function corrStbracket($level, $levelid = null)
{
$rateStbracket = [];
$attrition = [];
$rateStbracket = [];
$attrition = [];
$batches = [];
$results = Correlation::getStbracket($level, $levelid);
foreach ($results as $result) {
array_push($batches, $result->batch);
$rateStbracket[$result->batch] = $result->ratio;
$attrition[$result->batch] = $result->dropouts;
}
return round($this->getCorrelation($rateStbracket, $attrition, $batches), 2);
}