condition mean min max ZT0-3 7.820912 7.820912 7.820912 ZT4-7 7.6131815 7.6131815 7.6131815 ZT8-11 8.428329999999999 8.428329999999999 8.428329999999999 ZT12-15 7.973609 7.973609 7.973609 ZT16-19 7.428145499999999 7.428145499999999 7.428145499999999 ZT20-23 7.820912 7.820912 7.820912