condition mean min max ZT0-3 8.678749 8.678749 8.678749 ZT4-7 8.6915095 8.6915095 8.6915095 ZT8-11 8.247021499999999 8.247021499999999 8.247021499999999 ZT12-15 7.563100500000001 7.563100500000001 7.563100500000001 ZT16-19 8.740147 8.740147 8.740147 ZT20-23 8.425858 8.425858 8.425858