Hey, I am running into a problem answering the question in the title. All variables are numeric.

```
lm1 <- lm(y ~ x * z, data = data)
```

I have tried a pairwise t-test, but am unsure if this is the right approach, but I get an error message:

Error in unique.default(x, nmax = nmax) :

unique() applies only to vectors

Does anyone know how to do this?