Question 1200118
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I understand the reason of your dither: it is because you have a tendency to consider the set of observations as a function.


In reality, the set of observation is NOT NECESSARY a function: it is only a sequence of pairs (input,output)
without a requirement that every single input must have a unique output:
in different pairs, the output CAN BE DIFFERENT for the same input. 


I think it is a regular situation (not exclusive), when people work with observations.


A standard procedure of finding a linear regression allows such pairs and treats them with no problems: 
- it treats them as sequence of pairs, not as a function.



To check, I went to website 

https://www.graphpad.com/quickcalcs/linear1/


and used free of charge calculator for linear regression there.



I inputted their numbers as a table (as is), and got precisely the same linear regression formula as in the referred site

https://www.statology.org/residuals/


without any trouble.  It means that the procedure works/treats smoothly in such cases. 



So, my suggestion/conclusion/diagnosis is that it is a regular case: you should not be in trouble.



When you consider residuals, they are the differences between the real output of a pair 
and the prediction of the linear regression for this input value.



Again, for your better understanding: the observations are the set of pairs, not necessary a function,
while a regression is a real function.