public static function getGlobalPercentages($appId) {
        $params = ['gameid' => $appId];
        $data = WebApi::getJSONObject('ISteamUserStats', 'GetGlobalAchievementPercentagesForApp', 2, $params);

        $percentages = [];
        foreach($data->achievementpercentages->achievements as $achievementData) {
            $percentages[$achievementData->name] = (float) $achievementData->percent;
        }

        return $percentages;
    }