这是我的数据框：
rearing.temp<-c("15", "15", "15", "15", "15", "15", "15", "15", "19", "19", "19", "19", "19", "19", "19", "19")
source<-c("field", "field", "woods", "woods", "field", "field", "woods", "woods", "field", "field", "woods", "woods", "field", "field", "woods", "woods")
runway.temp<-c("40","20","40","20","40","20","40","20","40","20","40","20","40","20","40","20")
velocity<-c("2.3", "2.1", "1.9", "1.9", "2.3", "2.2", "2.3", "2.0", "1.1", "1.3", "3.2", "2.0", "2.0", "2.4", "2.2", "3.0")
snail<-data.frame(rearing.temp, source, runway.temp, velocity)
这是我的模型：
mod <- lm(velocity ~ runway.temp*source*rearing.temp, data=snail)
当我做一个emmeans对比时：
emmeans(mod, pairwise~runway.temp*source*rearing.temp)
我得到了 28 种不同的比较，但我只想查看在 40° 跑道温度下测试的 15° 饲养的田螺与在 40° 跑道温度下测试的 15° 饲养的木蜗牛的速度之间的差异。我只想对在相同温度下饲养的蜗牛进行一次比较，在相同温度下进行测试，但来自不同的栖息地。另外，当我进行所有 28 次比较时，它会剥夺统计能力，而且几乎所有内容都不重要。如何在不设置子集的情况下进行特定的成对比较？
谢谢，
里卡多