selectiongain (version 1.2.1.0)

multistageselection: Expected gain for k-stages selection (old function)

Description

This function calculates the well-known selection gain $\Delta G(y)$, which is described by Cochran (1951). For one-stage selection the gain is defined as $\Delta G (y) = i \rho_{y} \rho_{1}$, where $i$ is the selection intensity, $\rho_{1}$ is the correlation between the true breeding value and the selection index $y$ (Utz 1969). During a selection procedure, questions such as "How great is the yield after selection?" and "After three years testing and selection, how much is the chance that we miss one good candidate or the best candidate?" are frequently asked. These two questions can be answered by calculating the expected gain and variance of the gain, of a truncated multi-normal distribution (Tallis 1961). A numerical equation for calculating such moment generating function is since a long time available (Utz 1969). However, the properties of this old algorithm is limited. It is slow and can only handle a restricted selection model, which has at most three independent variables. We developed an R-package for maximizing the gain of a multi-stage selection procedure under certain restrictions, e.g., a given annual budget or certain risk limits of each stage. This package is applied in the fields of plant/animal breeding, where a multi-normal regression model is commonly built. It can handle a restricted selection model with up to eight independent variables within seconds. This is an old function, for R version

Usage

multistageselection(k, corr, alphaofx, sumdimofxandy,alg)

Arguments

sumdimofxandy

It is the dimension of k, which is dimension of x plus 1 (y has one dimension).

k

The lower bound of the integral, should be a vector. The first element of k is the lower bound of the response variable, Y, which is usually set as -Inf. The dimension of k should be the dimension of selection stage plus one.

corr

correlation matrix.

alphaofx

Selected fraction, this is a scalar not a vector.

alg

It decides which algorithm will be used, the Genz and Brett' algorithm is used by default. The Miwa's algorithm can be optional (Mi. et al. 2009; Genz. et al. 2010).

Value

• The value returned, is the gain of selection.

Details

There are only three functions in the package. The functions are used to calculate the moment generating function of the truncated multivariate normal distribution. The selection gain can be described as follow: $x_i=y+e_i$, where $x_i$: observed mean value of the character at the $i$th stage, $y$: the true genetic value which generates the observation, $e_i$: experiment error, which is assumed to be normally distributed. The true genetic value can be estimated by the observations with a regression function, $y(x)=f(x_1,x_2,...,x_i)$. A fraction $u$ is defined as the ratio of the variance of $e_1$ and $y$ Under the normality assumption, $y$ and $x_i$ are multivariate normally distributed. We want to maximize the expected value of $y$ in the restricted area, which is specified by the selection fraction. The Moment Generating Function (MGF) is used to calculate this multi-dimensional integral (Tallis, 1961; Utz, 1969). Computation of the expected value of $y$ requires computation of the following multi-dimensional integral over the restricted area defined by the selection. Let $\Omega={x_i \geq u_i; \, 1\leq i\leq k}$, $U={u_1,...,u_k}$, $\phi_k$: the density function of the multivariate normal distribution. The integral is given by $E_{\Omega}(y) = \int_{-\infty} ^\infty y(x) \int_0^\infty...\int_0^\infty \phi_k(X; U, \Sigma) \,dx_1...dx_k dy$ For further details about the whole project (selection gain for Double haploids and selection gain with markers), please contact the project contact person. The most important function is "multistageselection", which calculates the selection gain from given selection fraction and correlation matrix.

References

W.G. Cochran. Improvent by means of selection. In: Proceedings Second Berkeley Symposium on Math Stat Prof, pp449-470, 1951 G.M. Tallis. Moment generating function of truncated multi-normal distribution. Journal of the Royal Statistical Society, Series B, 23(1):223-229, 1961. H.F. Utz. Mehrstufenselecktion in der Pflanzenzuechtung. Doctor thesis, University Hohenheim, 1969. X. Mi, T. Miwa and T. Hothorn. Implement of Miwa's analytical algorithm of multi-normal distribution, R Journal, 1:37-39, 2009. A., Genz, F., Bretz. Computation of Multivariate Normal and t Probabilities. Lecture Notes in Statistics, Vol. 195, Springer-Verlag, Heidelberg, 2009 A., Genz, F., Bretz, T., Miwa, X., Mi, F., Leisch, F., Scheipl, T., Hothorn. mvtnorm: Multivariate normal and t distributions. R package version 0.9-9, 2010.

See Also

No link

Examples

##---- Should be DIRECTLY executable !! ----
##-- ==>  Define data, use random,
##--	or do  help(data=index)  for the standard data sets.


corr=diag(4)

corr12=0.3508
corr[1,2]=corr12
corr[2,1]=corr12

corr13=0.3508
corr[1,3]=corr13
corr[3,1]=corr13

corr14=0.4979
corr[1,4]=corr14
corr[4,1]=corr14

corr23=0.3016
corr[2,3]=corr23
corr[3,2]=corr23

corr24=0.5630
corr[2,4]=corr24
corr[4,2]=corr24

corr34=0.5630
corr[3,4]=corr34
corr[4,3]=corr34


quantile=c(0.4308,0.9804,1.8603)
k=c(-200,quantile)
# -200 is small enough to send the lower bound to be -Inf

alphaofx=pmvnorm(lower=c(-200,quantile),corr=corr)

multistageselection(k=c(-200,quantile),corr=corr,alphaofx,sumdimofxandy=4)



#####
# new code for adapt the window input of the red-R
#####

k=c(-200,0.4308,0.9804,1.8603)

corr=matrix( c(1,       0.3508,0.3508,0.4979,
               0.3508  ,1,     0.3016,0.5630,
               0.3508,  0.3016,1     ,0.5630,
               0.4979,  0.5630,0.5630,1), 
              nrow=4  
)

sumdimofxandy=4

alphaofx=pmvnorm(lower=k,corr=corr)

multistageselection(k=k,corr=corr,alphaofx,sumdimofxandy=4)