condition mean min max ZT0-3 8.188564 8.188564 8.188564 ZT4-7 7.595394 7.595394 7.595394 ZT8-11 8.2757995 8.2757995 8.2757995 ZT12-15 8.0986505 8.0986505 8.0986505 ZT16-19 7.739497999999999 7.739497999999999 7.739497999999999 ZT20-23 8.745759 8.745759 8.745759