condition mean min max ZT0-3 8.486616 8.486616 8.486616 ZT4-7 8.523518 8.523518 8.523518 ZT8-11 7.5880595 7.5880595 7.5880595 ZT12-15 7.604143499999999 7.604143499999999 7.604143499999999 ZT16-19 7.214569 7.214569 7.214569 ZT20-23 7.5049265 7.5049265 7.5049265