View source: R/tool_ranfixef.R

within_intercept | R Documentation |

This function gives an overall intercept for within models and its accompanying standard error or an within model with the overall intercept

```
within_intercept(object, ...)
## S3 method for class 'plm'
within_intercept(object, vcov = NULL, return.model = FALSE, ...)
```

`object` |
object of class |

`...` |
further arguments (currently none). |

`vcov` |
if not |

`return.model` |
a logical to indicate whether only the overall intercept
( |

The (somewhat artificial) intercept for within models (fixed
effects models) was made popular by Stata of StataCorp
\insertCite@see @GOUL:13plm, EViews of IHS, and gretl
\insertCite@see @GRETL:2021, p. 200-201, listing 23.1plm, see for
treatment in the literature,
e.g., \insertCiteGREE:12;textualplm, Ch. 11.4.4, p. 364. It can
be considered an overall intercept in the within model framework
and is the weighted mean of fixed effects (see **Examples** for the
relationship).

`within_intercept`

estimates a new model which is
computationally more demanding than just taking the weighted
mean. However, with `within_intercept`

one also gets the
associated standard error and it is possible to get an overall
intercept for twoway fixed effect models.

Users can set argument `vcov`

to a function to calculate a
specific (robust) varianceâ€“covariance matrix and get the
respective (robust) standard error for the overall intercept,
e.g., the function `vcovHC()`

, see examples for
usage. Note: The argument `vcov`

must be a function, not a
matrix, because the model to calculate the overall intercept for
the within model is different from the within model itself.

If argument `return.model = TRUE`

is set, the full model object is returned,
while in the default case only the intercept is returned.

Depending on argument `return.model`

: If `FALSE`

(default), a named
`numeric`

of length one: The overall intercept for the estimated within model
along attribute "se" which contains the standard error for the intercept.
If `return.model = TRUE`

, the full model object, a within model with the
overall intercept (NB: the model identifies itself as a pooling model, e.g.,
in summary()).

Kevin Tappe

`fixef()`

to extract the fixed effects of a within model.

```
data("Hedonic", package = "plm")
mod_fe <- plm(mv ~ age + crim, data = Hedonic, index = "townid")
overallint <- within_intercept(mod_fe)
attr(overallint, "se") # standard error
# overall intercept is the weighted mean of fixed effects in the
# one-way case
weighted.mean(fixef(mod_fe), pdim(mod_fe)$Tint$Ti)
### relationship of type="dmean", "level" and within_intercept
## one-way balanced case
data("Grunfeld", package = "plm")
gi <- plm(inv ~ value + capital, data = Grunfeld, model = "within")
fx_level <- fixef(gi, type = "level")
fx_dmean <- fixef(gi, type = "dmean")
overallint <- within_intercept(gi)
all.equal(overallint + fx_dmean, fx_level, check.attributes = FALSE) # TRUE
## two-ways unbalanced case
gtw_u <- plm(inv ~ value + capital, data = Grunfeld[-200, ], effect = "twoways")
int_tw_u <- within_intercept(gtw_u)
fx_dmean_tw_i_u <- fixef(gtw_u, type = "dmean", effect = "individual")[index(gtw_u)[[1L]]]
fx_dmean_tw_t_u <- fixef(gtw_u, type = "dmean", effect = "time")[index(gtw_u)[[2L]]]
fx_level_tw_u <- as.numeric(fixef(gtw_u, "twoways", "level"))
fx_level_tw_u2 <- int_tw_u + fx_dmean_tw_i_u + fx_dmean_tw_t_u
all.equal(fx_level_tw_u, fx_level_tw_u2, check.attributes = FALSE) # TRUE
## overall intercept with robust standard error
within_intercept(gi, vcov = function(x) vcovHC(x, method="arellano", type="HC0"))
## have a model returned
mod_fe_int <- within_intercept(gi, return.model = TRUE)
summary(mod_fe_int)
# replicates Stata's robust standard errors
summary(mod_fe_int, vcvov = function(x) vcovHC(x, type = "sss"))
```

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