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lbp@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




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Re: help

Thierry Onkelinx
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 [hidden email] <[hidden email]>:

> 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: [hidden email]
> Phone: 86 (25) 84396394
>
>         [[alternative HTML version deleted]]
>
> _______________________________________________
> R-sig-ecology mailing list
> [hidden email]
> https://stat.ethz.ch/mailman/listinfo/r-sig-ecology
>

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