Question

The function is part of $this and it passes in a MySQL query which has a few ? marks. The parameters get filled in through the execute and the results are being loaded into a separate object. Does this object (requesting the script) need to be passed in the runSelect() and does $STH really need to exist or can it be translated to a part of $this?

public function runSelect($query, $param, $obj){
    try {
        $STH = $this->dbh->prepare($query);
        $STH->setFetchMode(PDO::FETCH_INTO, $obj);
        $STH->execute($param);
        $STH->fetch();
    } catch(PDOException $e) {
        echo $e->getMessage();
    }
    return($obj);
}

Answer 1

Does this object (requesting the script) need to be passed in the runSelect()

No.

does $STH really need to exist

Yes.

can it be translated to a part of $this?

Yes.