ammistability (version 0.1.4)

SSI: Simultaneous Selection Indices for Yield and Stability

Description

SSI computes the Simultaneous Selection Index for Yield and Stability (SSI) according to the methods specified in the argument method.

Usage

SSI(y, sp, gen, method = c("farshadfar", "rao"), a = 1)

Value

A data frame with the following columns:

SP

The stability parameter values.

SSI

The computed values of simultaneous selection index for yield and stability.

rSP

The ranks of the stability parameter.

rY

The ranks of the mean yield of genotypes.

means

The mean yield of the genotypes.

The names of the genotypes are indicated as the row names of the data frame.

Arguments

y

A numeric vector of the mean yield/performance of genotypes.

sp

A numeric vector of the stability parameter/index of the genotypes.

gen

A character vector of the names of the genotypes.

method

The method for the computation of simultaneous selection index. Either "farshadfar" or "rao" (See Details).

a

The ratio of the weights given to the stability components for computation of SSI when method = "rao" (See Details).

Details

The SSI according to rao_use_2005;textualammistability (I_i) is computed as follows:

I_i = Y_iY_.. + 1SP_i1T_i=1^T1SP_i

Where SP_i is the stability measure of the ith genotype under AMMI procedure; Y_i is mean performance of ith genotype; Y_.. is the overall mean; T is the number of genotypes under test and is the ratio of the weights given to the stability components (w_2) and yield (w_1) with a restriction that w_1 + w_2 = 1. The weights can be specified as required.

	w_1	w_2
1.00	0.5	0.5
0.67	0.6	0.4
0.43	0.7	0.3
0.25	0.8	0.2

The SSI proposed by farshadfar_incorporation_2008;textualammistability is called the Genotype stability index (GSI) or Yield stability index (YSI) farshadfar_ammi_2011ammistability and is computed by summation of the ranks of the stability index/parameter and the ranks of the mean yields.

GSI = YSI = R_SP + R_Y

Where, R_SP is the stability parameter/index rank of the genotype and R_Y is the mean yield rank of the genotype.

References

See Also

AMGE.AMMI, ASI.AMMI, ASTAB.AMMI, AVAMGE.AMMI, DA.AMMI, DZ.AMMI, EV.AMMI, FA.AMMI, MASV.AMMI, SIPC.AMMI, ZA.AMMI

Examples

library(agricolae)
data(plrv)
model <- with(plrv, AMMI(Locality, Genotype, Rep, Yield, console=FALSE))

yield <- aggregate(model$means$Yield, by= list(model$means$GEN),
               FUN=mean, na.rm=TRUE)[,2]
stab <- DZ.AMMI(model)$DZ
genotypes <- rownames(DZ.AMMI(model))

# With default ssi.method (farshadfar)
SSI(y = yield, sp = stab, gen = genotypes)

# With  ssi.method = "rao"
SSI(y = yield, sp = stab, gen = genotypes, method = "rao")

# Changing the ratio of weights for Rao's SSI
SSI(y = yield, sp = stab, gen = genotypes, method = "rao", a = 0.43)