Hi

I have never seen germination experiments carried out as ordinal regression.

Most germination tests are done using a nls model.

For some species germination may only start a week after planting and then

germinate over 2 or 3 days.

If all germinated over the experimental period and there is no change in

germination between readings then read them accordingly.

If there are ungerminated seeds at the end; have these then had germinable

tests been applied to them?.

I agree with Thierry about survival analysis.

If however you are wanting to get into latency then ordinal models may be OK

Another package to do ordinal regression is VGAM

Regards

Duncan

Duncan Mackay

Department of Agronomy and Soil Science

University of New England

Armidale NSW 2351

Email: home:

[hidden email]
-----Original Message-----

From: R-help [mailto:

[hidden email]] On Behalf Of Bob O'Hara

Sent: Saturday, 16 January 2016 01:49

To: r-help

Subject: [R] Ordinal regression with some categories combined for some data

Hi!

I've been asked about a problem where I think I can see how to write

the model, but don't know if it's been implemented in R. It's not

something I work on a lot, so I'm hoping someone else can point me to

an answer straight away.

The researcher has been carrying out germination experiments: lost of

seeds are put in several conditions (temperature humidity etc.), and

every few days they are checked to see if they have germinated.

Because the days are discrete I think it makes sense to view this as

an ordinal regression problem (rather than as an interval censored

survival analysis). But what makes this tricky is that there are days

when the researcher only checked some seeds. So for some seeds the

germination might fall into more than one category.

Is there a package in R that can handle this, i.e. do an ordinal

regression where for some observations the categories are interval

censored? Or is it easier to go straight to a full interval-censored

survival analysis?

Bob

--

Bob O'Hara

Biodiversity and Climate Research Centre

Senckenberganlage 25

D-60325 Frankfurt am Main,

Germany

Tel: +49 69 798 40226

Mobile: +49 1515 888 5440

WWW:

http://www.bik-f.de/root/index.php?page_id=219Blog:

http://occamstypewriter.org/boboh/Journal of Negative Results - EEB: www.jnr-eeb.org

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