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I have data that measures the temperature of flowers and leaves on different plant species. These are the comparisons I am trying to make:

  1. Comparing the flower and leaf of the same plant at the same time of day
  2. Comparing the flower or leaf of a plant to the same flower or leaf at different times of day - on the same plant

My current interpretation is that 1 is an independent statistical test because while they are both on the same individual plant, they are separate "individuals" themselves. For 2 I believe it is a paired test as it is measuring the same flower or leaf at different times of day.

What is confusing me is that I have been taught that if it is the same "individual" then it should be paired, therefore 1 should be a paired test. However my interpretation is that "individual" means something different in the mathematical reality of the tests, where they are seen as different pools in this instance.

Am I correct in my thought? Or completely wrong?

Thank you

Edit: Maybe some clarification to my thought: The difference between my 2 tests is that one uses the same repeated leaf or flower (referring to case 2) at different times of day (therefore it is paired as it is a measurement of the same thing twice at different times). This contrasts with case 1 as this is comparing 2 different objects at the same time of day. The confusion for me comes in when case 1 is still on the same individual - they are related in a way, but I'm unsure if this is relevant to the test.

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  • $\begingroup$ Is your goal just to establish that the temperatures are different? $\endgroup$
    – mkt
    Sep 12, 2019 at 10:55
  • $\begingroup$ @mkt Yes. For 1 I want to establish if the flower and leaf are different temperatures from eachother. Then for 2 I want to establish if the flower or leaf change temperatures as evening arrives. They are both on the same plant (which is where I'm confused whether it is paired or not, due to them being on the same plant). $\endgroup$
    – s33ds
    Sep 12, 2019 at 12:58

1 Answer 1

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Assuming you sample 1 flower and 1 leaf from every plant, I would treat them as paired. And if you want to compare the leaf/flower from the same plant in morning vs. evening, I would again treat them as paired. Things are more complicated if you are sampling multiple flowers/leaves from each plant, or if you are using several time points, in which case you should use s to deal with the non-independence of data points sampled from the same individual.

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  • $\begingroup$ Luckily I am only measuring one flower and one leaf of the same plant. So just that I am sure (if you would please allow it to me!), measuring the temperature of a leaf vs a flower on a single plant would be the equivalent of measuring, e.g. the temperature of 2 different rooms in a house? They would be paired due to them being related by the same household $\endgroup$
    – s33ds
    Sep 12, 2019 at 13:31
  • $\begingroup$ @s33ds Yes, that's correct. The tag info and wikipedia pages about paired data have a bit more detail about the topic, if you are interested. $\endgroup$
    – mkt
    Sep 12, 2019 at 13:34

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