condition mean min max ZT0-3 6.642685 6.642685 6.642685 ZT4-7 7.866958 7.866958 7.866958 ZT8-11 7.8544485 7.8544485 7.8544485 ZT12-15 7.423041 7.423041 7.423041 ZT16-19 8.3019465 8.3019465 8.3019465 ZT20-23 8.073097 8.073097 8.073097