Calculate marginal effects of probit model with categorial data

Question

So my example data looks like this:

library(dplyr)
library(plm)
library(car)
library(margins)
test <- structure(list(period = c(1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 4, 
5, 5, 5, 6, 6, 6, 6, 7, 7, 8, 8, 8, 8, 9, 9, 9, 9, 10, 10, 10, 
10, 1, 2, 2, 2, 3, 3, 3, 3, 5, 6, 6, 7, 7, 7, 7, 8, 8), indicator = c(0L, 
0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 
0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 
0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 
1L)), row.names = c(NA, -50L), class = "data.frame")

In the next step I create different categories for the periodvariable

test$factor_period <-car::recode(test$period,"0:2='<2';3:5='3-5';6='6';7='7';8='8';9='9';10='10';11='11';12:44='>12'")

I am now calculating a probit model.

model_time <- glm(indicator ~ factor_period, family = binomial(link = "probit"), data = test)

So far so good. Now I am trying do determine the marginal effect of factor_period on indicator at factor_period = "8"like this:

res_time <- summary(margins(model = model_time, at = list(factor_period = "8"), data = test))

This returns the error message:

Error in attributes(.Data) <- c(attributes(.Data), attrib) : 
      'names'[1] attribute must be the same length as the vector[0]

It seems like categorizing the period data is the problem. Without the atargurment, the marginscommand works just fine...Does anyone know how to fix this?

Answer 1

Solution: By releveling factor_period to "8" you can avoid the atcommand in the marginsoperator and therefore calculate all marginal effects.

test$factor_period<-relevel(as.factor(test$factor_period), ref="8")