condition mean min max ZT0-3 7.085681 7.085681 7.085681 ZT4-7 7.4704975000000005 7.4704975000000005 7.4704975000000005 ZT8-11 7.582168 7.582168 7.582168 ZT12-15 7.4360325 7.4360325 7.4360325 ZT16-19 8.083518999999999 8.083518999999999 8.083518999999999 ZT20-23 7.6535340000000005 7.6535340000000005 7.6535340000000005