1278      * @param bool   $show_years
1282     private function averageLifespanQuery(string $sex, bool $show_years): string  argument
1288         if ($show_years) {
1298      * @param bool $show_years
1302     public function averageLifespan(bool $show_years): string  argument
1304         return $this->averageLifespanQuery('BOTH', $show_years);
1310      * @param bool $show_years
1314     public function averageLifespanFemale(bool $show_years): string  argument
1316         return $this->averageLifespanQuery('F', $show_years);
1322      * @param bool $show_years
1326     public function averageLifespanMale(bool $show_years): string  argument
1328         return $this->averageLifespanQuery('M', $show_years);