Returns a comparison of the WTP between a preference space and WTP space model.

`wtpCompare(model_pref, model_wtp, scalePar)`

- model_pref
The output of a "preference space" model estimated using the

`logitr()`

function.- model_wtp
The output of a "willingness to pay space" model estimated using the

`logitr()`

function.- scalePar
The name of the column that identifies the scale variable, which is typically "price" for WTP space models, but could be any continuous variable, such as "time".

A data frame comparing the WTP estimates from preference space and WTP space models.

Willingness to pay (WTP) is first computed from the preference space model by dividing the estimated parameters by the scale parameter (typically "price" to obtain WTP estimates). Then those estimates are compared against the WTP values directly estimated from the "WTP" space model. Uncertainty is handled via simulation.

```
library(logitr)
# Estimate a MNL model in the Preference space
mnl_pref <- logitr(
data = yogurt,
outcome = "choice",
obsID = "obsID",
pars = c("price", "feat", "brand")
)
#> Running model...
#> Done!
# Compute the WTP implied from the preference space model
wtp_mnl_pref <- wtp(mnl_pref, scalePar = "price")
# Estimate a MNL model in the WTP Space, using the computed WTP values
# from the preference space model as starting points
mnl_wtp <- logitr(
data = yogurt,
outcome = "choice",
obsID = "obsID",
pars = c("feat", "brand"),
scalePar = "price",
startVals = wtp_mnl_pref$Estimate
)
#> Running model...
#> Done!
# Compare the WTP between the two spaces
wtpCompare(mnl_pref, mnl_wtp, scalePar = "price")
#> pref wtp difference
#> scalePar 0.3665546 0.366589 0.00003448
#> feat 1.3406987 1.340815 0.00011655
#> brandhiland -10.1362190 -10.135947 0.00027163
#> brandweight -1.7490940 -1.749231 -0.00013707
#> brandyoplait 2.0038476 2.003530 -0.00031745
#> logLik -2656.8878790 -2656.887881 -0.00000180
```