condition mean min max ZT0-3 7.367633 7.367633 7.367633 ZT4-7 6.921817 6.921817 6.921817 ZT8-11 7.8245795000000005 7.8245795000000005 7.8245795000000005 ZT12-15 6.7967965 6.7967965 6.7967965 ZT16-19 7.932534 7.932534 7.932534 ZT20-23 7.290343 7.290343 7.290343