Parse 'yes' to bool

function parse_columnist_role($author_id) {
    /* See author_is_columnist, below.

    This function takes the string 'yes' or no' and parses it.
    I probably go overboard in sanitization, but I've seen the dedication
    of our local users.

    parse_columnist_role returns true if the string parses to 'yes' */
    $meta_tag = get_the_author_meta('columnist', $author_id);
    $is_columnist = false;

    if (!empty($meta_tag)) {
        $meta_tag = strtolower($meta_tag);
        $meta_tag = strip_tags($meta_tag);

        if (strpos('yes', $meta_tag) != -1) {
            $meta_tag = preg_replace('/([^yes].*$)/', '', $meta_tag);
        } else {
            $meta_tag = preg_replace('/([^no].*$)/', '', $meta_tag);
        }

        if ($meta_tag === 'yes') {
            $is_columnist = true;
        }
    }

    return $is_columnist;
}

function author_is_columnist() {
    /* We've (currently unused) added a flag to each user in order to indicate
    that they have a serial column.

    parse_columnist_role parses the variable string.
    author_is_columnist returns true or false. */
    $id = get_the_author_meta('ID');
    return parse_columnist_role($id);
}