><script src="../pkgdown.js"></script><meta property="og:title" content="Effect description — slope"><meta property="og:description" content='There is four ways that effects can be defined
in GRD. `"factor" = slope(s)` will vary the means by an amount of s for
each step of the factor; `"factor" = extent(s)` will vary the means
uniformly so that there is a difference of s between the first and
the last factor level; `"factor" = custom(a,b,c..)` will alter each
means by an amount of a for the first, b for t