condition mean min max ZT0-3 8.948263 8.948263 8.948263 ZT4-7 9.205872 9.205872 9.205872 ZT8-11 9.435705 9.435705 9.435705 ZT12-15 8.317402 8.317402 8.317402 ZT16-19 9.642308 9.642308 9.642308 ZT20-23 8.963227 8.963227 8.963227