Here comes my case:
I conducted an experiment with roughly the following design:
30 participants, each with a unique id, were asked to rank using a likert scale how much they liked images of forests. All the participants ranked the first 8 images and then the following 5 images were randomly drawn from a pool of 15 images. Therefore, in total each participant viewed 13 images of forests, but not all images were viewed by each participant. As the responses are ordinal I have gone with a cumulative link mixed effects model to preserve the structure of the data.
And here comes when I need your expertise. So far, I believe that the random terms of my model should take into account that:
Participants (id) Image (id)
However, Im confused about how to incorporate the random effects as each participants views some but not all of the same images. Thus-far I have come to the conclusion and coded it as:
clmm(likert_Rating ~ Experience + X.4 + X.3 + (1|part_id)+(1|Plot_ID), data=TotalF)
However, no matter how many models I try, I am never sure about what terms would be reasonable to include as randoms.
I would really appreciate if some of you could point me in the right direction as I am struggling to decide.
Many thanks for any help.
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