[R] normalmixEM gives widely divergent results.

[William Dunlap]

You could start by sorting the components, by lambda (size) or by mu (mean)
since, if you don't supply starting values, the order of the components is
random.  You could use the following to sort normalmixEM's output:

sort.mixEM <- function (x, decreasing = FALSE, ..., by = "lambda")
{
    stopifnot(inherits(x, "mixEM"), is.element(by, names(x)))
    o <- order(x[[by]], decreasing = decreasing)
    x$lambda <- x$lambda[o]
    x$sigma <- x$sigma[o]
    x$mu <- x$mu[o]
    x$posterior[] <- x$posterior[, o, drop = FALSE]
    x
}


Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Wed, Jan 27, 2016 at 8:51 AM, John Sorkin <JSorkin at grecc.umaryland.edu>
wrote:

> I am running normalmixEM:
> mixmdlscaled <- normalmixEM(data$FCWg)
> summary(mixmdlscaled)
> plot(mixmdlscaled,which=2)
>
> If I run the program multiple times, I get widely different results:
>
> > mixmdlscaled <- normalmixEM(data$FCWg)
> number of iterations= 41
> > summary(mixmdlscaled)
> summary of normalmixEM object:
>           comp 1   comp 2
> lambda 0.0818928 0.918107
> mu     0.6575938 0.740870
> sigma  0.0070562 0.178410
> loglik at estimate:  56.87445
> > plot(mixmdlscaled,which=2)
> > mixmdlscaled <- normalmixEM(data$FCWg)
> number of iterations= 357
> > summary(mixmdlscaled)
> summary of normalmixEM object:
>          comp 1    comp 2
> lambda 0.959912 0.0400879
> mu     0.722022 1.0220719
> sigma  0.165454 0.0131391
> loglik at estimate:  53.66051
> > plot(mixmdlscaled,which=2)
>
>
>
> I understand that when run without specifying various parameters (e.g. mu,
> or sigma) values are chosen randomly from a normal distribution with
> center(s) determined from binning the data. Despite this, would not one
> expect the results to be similar? If one is not to expect similar results,
> how can I get a solution in which I can have confidence? Should I run the
> program multiple times and take the average of the results? Should I look
> for the solution with the best log likelihood?
>
> Thank you,
> John
> John David Sorkin M.D., Ph.D.
> Professor of Medicine
> Chief, Biostatistics and Informatics
> University of Maryland School of Medicine Division of Gerontology and
> Geriatric Medicine
> Baltimore VA Medical Center
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> (Phone) 410-605-7119
> (Fax) 410-605-7913 (Please call phone number above prior to faxing)
>
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