condition mean min max ZT0-3 2.357273333333333 2.23791 2.591285 ZT4-7 2.439265 2.439265 2.439265 ZT8-11 2.6228499999999997 2.6228499999999997 2.6228499999999997 ZT12-15 3.6870775 3.6542 3.719955 ZT16-19 3.4001200000000003 3.4001200000000003 3.4001200000000003 ZT20-23 3.437525 3.437525 3.437525