condition mean min max ZT0-3 6.514077 6.514077 6.514077 ZT4-7 7.174147 7.174147 7.174147 ZT8-11 6.261846 6.261846 6.261846 ZT12-15 7.0048604999999995 7.0048604999999995 7.0048604999999995 ZT16-19 7.30745 7.30745 7.30745 ZT20-23 7.4173290000000005 7.4173290000000005 7.4173290000000005