condition mean min max ZT0-3 2.1 2.1 2.1 ZT4-7 21.8 21.8 21.8 ZT8-11 16.7 16.7 16.7 ZT12-15 6.1 6.1 6.1 ZT16-19 7.699999999999999 7.699999999999999 7.699999999999999 ZT20-23 18.25 18.25 18.25