condition mean min max ZT0-3 7.671887 7.671887 7.671887 ZT4-7 8.557056 8.557056 8.557056 ZT8-11 7.6303835 7.6303835 7.6303835 ZT12-15 8.257889 8.257889 8.257889 ZT16-19 8.133417000000001 8.133417000000001 8.133417000000001 ZT20-23 7.2052185 7.2052185 7.2052185