condition mean min max ZT0-3 7.499408 7.499408 7.499408 ZT4-7 9.11157 9.11157 9.11157 ZT8-11 8.768861999999999 8.768861999999999 8.768861999999999 ZT12-15 9.4931825 9.4931825 9.4931825 ZT16-19 8.552481499999999 8.552481499999999 8.552481499999999 ZT20-23 7.931868 7.931868 7.931868