condition mean min max ZT0-3 3.692665 3.692665 3.692665 ZT4-7 3.785735 3.785735 3.785735 ZT8-11 5.6048849999999995 5.6048849999999995 5.6048849999999995 ZT12-15 6.055285 6.055285 6.055285 ZT16-19 7.3538499999999996 7.3538499999999996 7.3538499999999996 ZT20-23 3.631025 3.631025 3.631025