      hp     wt
##  0.5156 0.05151 -12.24</code></pre>
<p>Note that some other packages available for R, as well as Stata’s <code>margins</code> and <code>mfx</code> packages enable calculation of so-called “marginal effects at means” (i.e., the marginal effect for a single observation that has covariate values equal to the means of the sample as a whole). The substantive interpretation of these is fairly ambiguous. While it was once common practice to estimate MEMs - rather than AMEs or MERs - this i