condition mean min max ZT0-3 2.1257733333333335 1.188015 3.03524 ZT4-7 0.848833 0.848833 0.848833 ZT8-11 0.970709 0.970709 0.970709 ZT12-15 3.1403675 2.7532249999999996 3.5275100000000004 ZT16-19 4.03886 4.03886 4.03886 ZT20-23 3.705875 3.705875 3.705875