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Generalized additive model for location, scale and shape : ウィキペディア英語版
Generalized additive model for location, scale and shape

In statistics, the Generalized Additive Model for Location, Scale and Shape (GAMLSS) is a class of statistical model developed by Rigby and Stasinopoulos. These models provide extended capabilities beyond the simpler generalized linear models and generalized additive models. These simpler models allow the typical values of a quantity being modelled to be related to whatever explanatory variables are available. Here the "typical value" is more formally a location parameter, which only describes a limited aspect of the probability distribution of the dependent variable. The GAMLSS approach allows other parameters of the distribution to be related to the explanatory variables; where these other parameters might be interpreted as scale and shape parameters of the distribution, although the approach is not limited to such parameters.
==Overview of the model==
The generalized additive model for location, scale and shape (GAMLSS) is a statistical model developed by Rigby and Stasinopoulos and later expanded to overcome some of the limitations associated with the popular generalized linear models (GLMs) and generalized additive models (GAMs). For an overview of these limitations see Nelder and Wedderburn (1972) and Hastie and Tibshirani's book.
In GAMLSS the exponential family distribution assumption for the response variable, (y), (essential in GLMs and GAMs), is relaxed and replaced by a general distribution family, including highly skew and/or kurtotic continuous and discrete distributions.
The systematic part of the model is expanded to allow modeling not only of the mean (or location) but other parameters of the distribution of ''y'' as linear and/or nonlinear, parametric and/or additive non-parametric functions of explanatory variables and/or random effects.
GAMLSS is especially suited for modelling a leptokurtic or platykurtic and/or positively or negatively skewed response variable. For count type response variable data it deals with over-dispersion by using proper over-dispersed discrete distributions. Heterogeneity also is dealt with by modelling the scale or shape parameters using explanatory variables. There are several packages written in R related to GAMLSS models.〔
A GAMLSS model assumes independent observations y_i for i = 1, 2, \dots , n
with probability (density) function f (y_i | \mu_i , \sigma_i , \nu_i , \tau_i ) conditional on (\mu_i , \sigma_i , \nu_i , \tau_i ) a vector of four distribution parameters, each of which can be a function to the explanatory variables. The first two population distribution parameters \mu_i and \sigma_i are usually characterized as location and scale parameters, while the remaining parameter(s), if any, are characterized as shape parameters, e.g. skewness and kurtosis parameters, although the model may be applied more generally to the parameters of any population distribution with up to four distribution parameters, and can be generalized to more than four distribution parameters.
:
\begin
g_1 (\mu) = \eta_1= X_1 \beta_1 + \sum_^ _(x_) \\
g_2(\sigma) = \eta_2= X_2 \beta_2 + \sum_^_(x_) \\
g_3(\nu) = \eta_3 = X_3 \beta_3 + \sum_^_(x_) \\
g_4(\tau)=\eta_4=X_4 \beta_4 + \sum_^_(x_)
\end

where μ, σ, ν, τ and \eta_k are vectors of length n, \beta^_k = (\beta_,\beta_,\ldots,\beta_) is a parameter vector of length J'_k, X_k is a fixed known design matrix of order n \times J'_k and h_ is a smooth non-parametric function of explanatory variable x_, j=1,2,\ldots, J_ and k=1,2,3,4.
For centile estimation the (WHO Multicentre Growth Reference Study Group ) have recommended GAMLSS and the Box-Cox power exponential (BCPE) distributions〔 for the construction of the WHO Child Growth Standards.〔WHO Multicentre Growth Reference Study Group (2006) WHO Child Growth Standards: Length/height-for-age, weight-for-age, weight-for-length, weight-for-height and body mass index-for-age: Methods and development. Geneva: World Health Organization.〕

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