condition mean min max ZT0-3 6.93947 6.93947 6.93947 ZT4-7 7.126086666666667 7.126086666666667 7.126086666666667 ZT8-11 7.14312 7.14312 7.14312 ZT12-15 7.0985000000000005 7.0985000000000005 7.0985000000000005 ZT16-19 7.1714400000000005 7.1714400000000005 7.1714400000000005 ZT20-23 7.22196 7.22196 7.22196