php - Getting the sum of columns in a Laravel raw select statement

I am trying to get the sum of the records that are returned in a Laravel select statement but I can't seem to get it right.

My original statement is as follows;

$results = DB::table('polls')->select('polls.id as poll_id', 'poll_votes.vote_count as vote_count', 'poll_options.id as poll_option_id')
    ->join('poll_options','polls.id','=','poll_options.poll_id')
    ->join('poll_votes', 'poll_options.id', '=', 'poll_votes.poll_option_id')
    ->where([['polls.status','=','1'], ['poll_options.status','=','1'],])
    ->get();
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I have tried adding the following after the last element on the->select line but I keep getting errors;

DB::raw('sum(poll_votes.vote_count) total_votes')
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Any help would be greatly appreciated