nobs.plm: Extract Total Number of Observations Used in Estimated Panelmodel

Description

This function extracts the total number of 'observations' from a fitted panel model.

Usage

# S3 method for panelmodel
nobs(object, ...)
# S3 method for pgmm
nobs(object, ...)

Arguments

object

a panelmodel object for which the number of total observations is to be extracted,

…

further arguments.

Value

A single number, normally an integer.

Details

The number of observations is usually the length of the residuals vector. Thus, nobs gives the number of observations actually used by the estimation procedure. It is not necessarily the number of observations of the model frame (number of rows in the model frame), because sometimes the model frame is further reduced by the estimation procedure. This is e.g. the case for first--difference models estimated by plm(…{}, model = "fd") where the model frame does not yet contain the differences (see also Examples).

Examples

Run this code

# NOT RUN {
# estimate a panelmodel
data("Produc", package = "plm")
z <- plm(log(gsp)~log(pcap)+log(pc)+log(emp)+unemp,data=Produc,
         model="random", subset = gsp > 5000)
         
nobs(z)       # total observations used in estimation
pdim(z)$nT$N  # same information
pdim(z)       # more information about the dimensions (no. of individuals and time periods)

# illustrate difference between nobs and pdim for first-difference model
data("Grunfeld", package = "plm")
fdmod <- plm(inv ~ value + capital, data = Grunfeld, model = "fd")
nobs(fdmod)      # 190
pdim(fdmod)$nT$N # 200

# }