condition mean min max ZT0-3 18.469957 18.469957 18.469957 ZT4-7 18.191293 18.191293 18.191293 ZT8-11 16.7658005 16.7658005 16.7658005 ZT12-15 15.528639499999999 15.528639499999999 15.528639499999999 ZT16-19 18.760167000000003 18.760167000000003 18.760167000000003 ZT20-23 19.2499465 19.2499465 19.2499465