twostage.lvmfit {lava} | R Documentation

## Two-stage estimator (non-linear SEM)

### Description

Two-stage estimator for non-linear structural equation models

### Usage

    ## S3 method for class 'lvmfit'
    twostage(object, model2, data = NULL,
      predict.fun = function(mu, var, data, ...) cbind(u1 = mu[, 1], u2 = mu[,
      1]^2 + var[1]), id1 = NULL, id2 = NULL, all = FALSE, formula = NULL,
      std.err = TRUE, ...)

### Arguments

`object` | Stage 1 measurement model
`model2` | Stage 2 SEM
`data` | data.frame
`predict.fun` | Prediction of latent variable
`id1` | Optional id-variable (stage 1 model)
`id2` | Optional id-variable (stage 2 model)
`all` | If TRUE return additional output (naive estimates)
`formula` | optional formula specifying non-linear relation
`std.err` | If FALSE calculations of standard errors will be skipped
`...` | Additional arguments to lower level functions

### Examples

    m <- lvm(c(x1,x2,x3)~f1,f1~z,
             c(y1,y2,y3)~f2,f2~f1+z)
    latent(m) <- ~f1+f2
    d <- simulate(m,100,p=c("f2,f2"=2,"f1,f1"=0.5),seed=1)

    ## Full MLE
    ee <- estimate(m,d)

    ## Manual two-stage
    ## Not run:
    m1 <- lvm(c(x1,x2,x3)~f1,f1~z); latent(m1) <- ~f1
    e1 <- estimate(m1,d)
    pp1 <- predict(e1,f1~x1+x2+x3)

    d$u1 <- pp1[,]
    d$u2 <- pp1[,]^2+attr(pp1,"cond.var")[1]
    m2 <- lvm(c(y1,y2,y3)~eta,c(y1,eta)~u1+u2+z); latent(m2) <- ~eta
    e2 <- estimate(m2,d)

    ## End(Not run)

    ## Two-stage
    m1 <- lvm(c(x1,x2,x3)~f1,f1~z); latent(m1) <- ~f1
    m2 <- lvm(c(y1,y2,y3)~eta,c(y1,eta)~u1+u2+z); latent(m2) <- ~eta
    pred <- function(mu,var,data,...)
        cbind("u1"=mu[,1],"u2"=mu[,1]^2+var[1])
    (mm <- twostage(m1,model2=m2,data=d,predict.fun=pred))

    if (interactive()) {
        pf <- function(p) p["eta"]+p["eta~u1"]*u + p["eta~u2"]*u^2
        plot(mm,f=pf,data=data.frame(u=seq(-2,2,length.out=100)),lwd=2)
    }

    ## Splines
    f <- function(x) cos(2*x)+x+-0.25*x^2
    m <- lvm(x1+x2+x3~eta1, y1+y2+y3~eta2, latent=~eta1+eta2)
    functional(m, eta2~eta1) <- f
    d <- sim(m,500,seed=1,latent=TRUE)
    m1 <- lvm(x1+x2+x3~eta1,latent=~eta1)
    m2 <- lvm(y1+y2+y3~eta2,latent=~eta2)
    mm <- twostage(m1,m2,formula=eta2~eta1,type="spline")
    if (interactive()) plot(mm)

    nonlinear(m2,type="quadratic") <- eta2~eta1
    a <- twostage(m1,m2,data=d)
    if (interactive()) plot(a)

    kn <- c(-1,0,1)
    nonlinear(m2,type="spline",knots=kn) <- eta2~eta1
    a <- twostage(m1,m2,data=d)
    x <- seq(-3,3,by=0.1)
    y <- predict(a, newdata=data.frame(eta1=x))

    if (interactive()) {
      plot(eta2~eta1, data=d)
      lines(x,y, col="red", lwd=5)

      p <- estimate(a,f=function(p) predict(a,p=p,newdata=x))$coefmat
      plot(eta2~eta1, data=d)
      lines(x,p[,1], col="red", lwd=5)
      confband(x,lower=p[,3],upper=p[,4],center=p[,1], polygon=TRUE, col=Col(2,0.2))

      l1 <- lm(eta2~splines::ns(eta1,knots=kn),data=d)
      p1 <- predict(l1,newdata=data.frame(eta1=x),interval="confidence")
      lines(x,p1[,1],col="green",lwd=5)
      confband(x,lower=p1[,2],upper=p1[,3],center=p1[,1], polygon=TRUE, col=Col(3,0.2))
    }

    ## Not run:  ## Reduce timing
     ## Cross-validation example
     ma <- lvm(c(x1,x2,x3)~u,latent=~u)
     ms <- functional(ma, y~u, f=function(x) -.4*x^2)
     d <- sim(ms,500)#,seed=1)
     ea <- estimate(ma,d)

     mb <- lvm()
     mb1 <- nonlinear(mb,type="linear",y~u)
     mb2 <- nonlinear(mb,type="quadratic",y~u)
     mb3 <- nonlinear(mb,type="spline",knots=c(-3,-1,0,1,3),y~u)
     mb4 <- nonlinear(mb,type="spline",knots=c(-3,-2,-1,0,1,2,3),y~u)
     ff <- lapply(list(mb1,mb2,mb3,mb4),
          function(m) function(data,...) twostage(ma,m,data=data,st.derr=FALSE))
     a <- cv(ff,data=d,rep=1,mc.cores=1)
     a

    ## End(Not run)

[Package lava version 1.5.1 Index]