Database table not updating properly from PHP website code

I am adding straw polls to a website using this tutorial: http://ift.tt/1TyVQdx

I have modified this code so I can create my own polls by entering the poll title and questions which gets stored in a database table. This table is then queried and the polls are loaded from the database. This is working fine, however, when I am trying to return the number of votes for each question the value is coming back 0 every time. The table 'tally' holds the question id, answer id and number of votes.

When I try to insert data into this tally table from the webPoll class, both the QID and AID rows are blank, only the votes value increments each time.

My database is MySQL, the tutorial I followed was to insert data into an SQLite DB, I think this might be the problem but I can't seem to find a solution as of yet.

In summary, I need to get the insert statements in the webPoll class inserting QID, AID & votes values as QID and AID are not inserting.

tally

CREATE TABLE tally (
        QID varchar(32) NOT NULL,
        AID integer NOT NULL,
        votes integer NOT NULL,
        PRIMARY KEY (QID,AID))

webPoll Class

$mysql_host = "localhost";
$mysql_database = "vote";
$mysql_user = "root";
$mysql_password = "";


class webPoll {

# makes some things more readable later
const POLL = true;
const VOTES = false;

# number of pixels for 1% on display bars
public $scale = 2;


public $question = '';
public $answers = array();
private $header = '<form class="webPoll" method="post" action="%src%">
                   <input type="hidden" name="QID" value="%qid%" />
                   <h4>%question%</h4>
                   <fieldset><ul>';
private $center = '';
private $footer = "\n</ul></fieldset>%button%\n</form>\n";
private $button = '<p class="buttons"><button type="submit" class="vote">Vote!</button></p>';
private $md5 = '';

/**
 * ---
 * Takes an array containing the question and list of answers as an
 * argument. Creates the HTML for either the poll or the results depending
 * on if the user has already voted
 */
public function __construct($params) {
$this->question = array_shift($params);
$this->answers = $params;
$this->md5 = md5($this->question);  

$this->header = str_replace('%src%', $_SERVER['SCRIPT_NAME'], $this-  >header);
$this->header = str_replace('%qid%', $this->md5, $this->header);
$this->header = str_replace('%question%', $this->question, $this->header);

# seperate cookie for each individual poll
isset($_COOKIE[$this->md5]) ? $this->poll(self::VOTES) : $this- >poll(self::POLL);    
}
private function poll($show_poll) {
$replace = $show_poll ? $this->button : '';
$this->footer = str_replace('%button%', $replace, $this->footer);

# static function doesn't have access to instance variable
if(!$show_poll) {
    $results = webPoll::getData($this->md5);
    $votes = array_sum($results);
}

for( $x=0; $x<count($this->answers); $x++ ) {
    $this->center .= $show_poll ? $this->pollLine($x) : $this->voteLine($this->answers[$x],$results[$x],$votes);
}

echo $this->header, $this->center, $this->footer;
}
private function pollLine($x) {
isset($this->answers[$x+1]) ? $class = 'bordered' : $class = '';
return "
<li class='$class'>
        <label class='poll_active'>
        <input type='radio' name='AID' value='$x' />
            {$this->answers[$x]}
        </label>
</li>
";
}
private function voteLine($answer,$result,$votes) {
$result = isset($result) ? $result : 0;
$percent = round(($result/$votes)*100);
$width = $percent * $this->scale;
return "
<li>
        <div class='result' style='width:{$width}px;'>&nbsp;</div>    {$percent}%
        <label class='poll_results'>
            $answer
        </label>
</li>
";
}
/**
 * processes incoming votes. votes are identified in the database by a     combination
 * of the question's MD5 hash, and the answer # ( an int 0 or greater ).
 */
static function vote() {
if(!isset($_POST['QID']) ||
!isset($_POST['AID']) ||
isset($_COOKIE[$_POST['QID']])) {
    return;
}
try{
$dbh = new PDO('mysql:host=localhost;dbname=vote', 'root', ''); 
$dbh->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );
} catch(PDOException $e) {
    echo "Error: " . $e->getMessage() . "<br/>";
    }

try {
    $sth = $dbh->prepare("INSERT INTO tally (QID,AID,votes) values ('QID',     'AID', '1')" );
    $sth->execute(array($_POST['QID'],$_POST['AID']));
}
catch(PDOException $e) {
    # 23000 error code means the key already exists, so UPDATE! 
    if($e->getCode() == 23000) {
        try {
            $sth = $dbh->prepare("UPDATE tally SET votes = votes + 1 WHERE     QID='$QID' AND AID='$AID'");
            $sth->execute(array($_POST['QID'],$_POST['AID']));
        }
        catch(PDOException $e) {
            webPoll::db_error($e->getMessage());
        }
    }
    else {
        webPoll::db_error($e->getMessage());
    }
}

# entry in $_COOKIE to signify the user has voted, if he has
if($sth->rowCount() == 1) {
    setcookie($_POST['QID'], 1, time()+60*60*24*365);
    $_COOKIE[$_POST['QID']] = 1;
}
}
static function getData($question_id) {
try {
    $dbh = new PDO('mysql:host=localhost;dbname=vote', 'root', ''); 
    $dbh->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );

    $STH = $dbh->prepare('SELECT AID, votes FROM tally WHERE QID = ?');
    $STH->execute(array($question_id));
}
catch(PDOException $e) {  
    # Error getting data, just send empty data set
    webPoll::db_error($e->getMessage());
    return array(0); 
}

while($row = $STH->fetch()) {
    $results[$row['AID']] = $row['votes'];   
}

return $results;
}
/*
 * You can do something with the error message if you like. Email yourself
 * so you know something happened, or make an entry in a log
 */
static function db_error($error) {   
echo "A database error has occured. $error";
exit;
}   
}