30  FAQ

30.1 Stack Overflow questions

• plot_predictions() over a range of unobserved values
• Plot the marginal effects from a plm package model
• Models with demeaned, polynomials, or transformed variables

30.2 Calling marginaleffects in functions, loops, environments, or after re-assigning variables

Functions from the marginaleffects package can sometimes fail when they are called inside a function, loop, or other environments. To see why, it is important to know that marginaleffects often needs to operate on the original data that was used to fit the model. To extract this original data, we use the get_data() function from the insight package.

In most cases, get_data() can extract the data which is stored inside the model object created by the modeling package. However, some modeling packages do not save the original data in the model object (in order to save memory). In those cases, get_data() will parse the call to find the name of the data object, and will search for that data object in the global environment. When users fit models in a different environment (e.g., function calls), get_data() may not be able to retrieve the original data.

A related problem can arise if users fit a model, but then assign a new value to the variable that used to store the dataset.

Recommendations:

1. Supply your dataset explicitly to the newdata argument of slopes() functions.
2. Avoid assigning a new value to a variable that you use to store a dataset for model fitting.