condition mean min max ZT0-3 7.03877 7.03877 7.03877 ZT4-7 6.22851 6.22851 6.22851 ZT8-11 6.41202 6.41202 6.41202 ZT12-15 6.94254 6.94254 6.94254 ZT16-19 7.239006666666667 7.239006666666667 7.239006666666667 ZT20-23 7.2242500000000005 7.2242500000000005 7.2242500000000005