Description Usage Arguments Details Value Note Author(s) References See Also Examples
The function NOF()
defines a normal distribution family, which has three parameters. The distribution
can be used in a GAMLSS fitting using the function gamlss()
.
The mean of NOF
is equal to mu
. The variance is equal to sigma^2*mu^nu
so
the standard deviation is sigma*mu^(nu/2)
. The function is design for cases where the
variance is proportional to a power of the mean.
The functions dNOF
, pNOF
, qNOF
and rNOF
define the density, distribution function,
quantile function and random
generation for the NOF
parametrization of the normal distribution family.
1 2 3 4 5 |
mu.link |
Defines the |
sigma.link |
Defines the |
nu.link |
Defines the |
x,q |
vector of quantiles |
mu |
vector of location parameter values |
sigma |
vector of scale parameter values |
nu |
vector of power parameter values |
log, log.p |
logical; if TRUE, probabilities p are given as log(p). |
lower.tail |
logical; if TRUE (default), probabilities are P[X <= x], otherwise, P[X > x] |
p |
vector of probabilities. |
n |
number of observations. If |
The parametrization of the normal distribution given in the function NOF()
is
f(y|mu,sigma,nu)=(1/(sqrt(2*pi)*sigma*mu^(nu/2)))* exp(-0.5*((y-mu)^2/sigma^2*mu^nu))
for y=(-Inf,Inf), μ=(-Inf,Inf), σ>0 and ν=(-Inf,+Inf).
returns a gamlss.family
object which can be used to fit a normal distribution family
in the gamlss()
function.
For the function NOF()
, mu is the mean and sigma*mu^(nu/2)
is the standard deviation of the normal distribution family.
The NOF is design for fitting regression type models where the variance is proportional to a power ofthe mean.
Models of this type are related to the "pseudo likelihood" models of Carroll and Rubert (1987) but here a proper
likelihood is miximised.
Note that because the high correlation between the sigma
and the nu
parameter the mixed()
method should be used in the fitting.
Mikis Stasinopoulos, Bob Rigby and Calliope Akantziliotou
Davidian, M. and Carroll, R. J. (1987), Variance Function Estimation, Journal of the American Statistical Association, Vol. 82, pp. 1079-1091
Rigby, R. A. and Stasinopoulos D. M. (2005). Generalized additive models for location, scale and shape,(with discussion), Appl. Statist., 54, part 3, pp 507-554.
Stasinopoulos D. M., Rigby R.A. and Akantziliotou C. (2006) Instructions on how to use the GAMLSS package in R. Accompanying documentation in the current GAMLSS help files, (see also http://www.gamlss.com/).
Stasinopoulos D. M. Rigby R.A. (2007) Generalized additive models for location scale and shape (GAMLSS) in R. Journal of Statistical Software, Vol. 23, Issue 7, Dec 2007, http://www.jstatsoft.org/v23/i07.
1 2 3 4 5 6 7 8 9 10 | NOF()# gives information about the default links for the normal distribution family
# library(gamlss)
#data(abdom)
## the normal distribution fit with constant sigma
#m1<-gamlss(y~poly(x,2), sigma.fo=~1, family=NO, data=abdom)
## the normal family fit with variance proportional to mu
#m2<-gamlss(y~poly(x,2), sigma.fo=~1, family=NOF, data=abdom, method=mixed(1,20))
## a nornal distribution fit with variance as a function of x
#m3 <-gamlss(y~poly(x,2), sigma.fo=~x, family=NO, data=abdom, method=mixed(1,20))
#GAIC(m1,m2,m3)
|
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