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Today's Topics:
1. help (lbp at njau.edu.cn)
2. Re: help (Thierry Onkelinx)
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Message: 1
Date: Thu, 19 May 2016 08:39:33 +0800
From: "lbp at njau.edu.cn" <lbp at njau.edu.cn>
To: r-sig-ecology <r-sig-ecology at r-project.org>
Subject: [R-sig-eco] help
Message-ID: <201605190839272047103 at njau.edu.cn>
Content-Type: text/plain; charset="UTF-8"
Now I have difficulty to choose between two modelling approach. Here is th story. To examine the clutch size laid by a parasitic wasp into caterpillar hosts which varies in age and size, we exposed individual larvae of three stages, after individually weighed, to parasitism, and the number of wasps emerged from each host (brood size) was recorded. Because host size and stage are mutually counfounding factors, the older the bigger, I have two modelling choices to separate the effect of stage and size. One is to make separate analyses, first analyzing the effct of stages in a model without the variable size, and then analyze the effect of the size under each stgae (several models); another approach is to make one analysis, put stage and size together in the same model to evaluate their separate and interacted effects on brood size. For the later approach, the variable size actualy contains the inflormation about the stage, thus violating the independence assumation. I am won!
dering which appraoch is approriate.
Thanks for any help.
Baoping
E-mail: lbp at njau.edu.cn
Phone: 86 (25) 84396394
[[alternative HTML version deleted]]
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Message: 2
Date: Thu, 19 May 2016 09:55:16 +0200
From: Thierry Onkelinx <thierry.onkelinx at inbo.be>
To: "lbp at njau.edu.cn" <lbp at njau.edu.cn>
Cc: r-sig-ecology <r-sig-ecology at r-project.org>
Subject: Re: [R-sig-eco] help
Message-ID:
<CAJuCY5wP7bdpDX6pPm2t6us1Zgsm0OnhDK0Z_Ji=EBr_BmX+Sg at mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
Dear Baoping,
You could standardize the weight by stage. That would remove the
confounding between weight and stage.
Best regards,
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature and
Forest
team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
Kliniekstraat 25
1070 Anderlecht
Belgium
To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to say
what the experiment died of. ~ Sir Ronald Aylmer Fisher
The plural of anecdote is not data. ~ Roger Brinner
The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of data.
~ John Tukey
2016-05-19 2:39 GMT+02:00 lbp at njau.edu.cn <lbp at njau.edu.cn>:
Now I have difficulty to choose between two modelling approach. Here is th
story. To examine the clutch size laid by a parasitic wasp into caterpillar
hosts which varies in age and size, we exposed individual larvae of three
stages, after individually weighed, to parasitism, and the number of wasps
emerged from each host (brood size) was recorded. Because host size and
stage are mutually counfounding factors, the older the bigger, I have two
modelling choices to separate the effect of stage and size. One is to make
separate analyses, first analyzing the effct of stages in a model without
the variable size, and then analyze the effect of the size under each stgae
(several models); another approach is to make one analysis, put stage and
size together in the same model to evaluate their separate and interacted
effects on brood size. For the later approach, the variable size actualy
contains the inflormation about the stage, thus violating the independence
assumation. I am won!
dering which appraoch is approriate.
Thanks for any help.
Baoping
E-mail: lbp at njau.edu.cn
Phone: 86 (25) 84396394
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