I'm not sure which method to use to model the relationship between two variables ($x$ and $y$) in the experiment described as follows:
- There are 3 variables: $x_{aim}$, $x$ and $y$.
- The value of $x_{aim}$ is set when operating the experiment. However, $x$ and $x_{aim}$ aren't always equal.
- The Pearson's correlation coefficient between $x_{aim}$ and $x$ is about 0.9.
- The Pearson's correlation coefficient between $x$ and $y$ is much less: about 0.5.
- $y$ has a maximum possible value ($y_{max}$) which can't be exceeded.
- Each data point is obtained after setting $x_{aim}$ and reading $x$ and $y$.
Although the Pearson's correlation coefficient between $x$ and $y$ isn't great, it looks like $y$ tends to increase with $x$.
After doing simple linear regressions of $y=f(x)$ and $x=g(y)$ (and converting the latter back as $g^{-1}$, so as to be displayed on the same graph as $f$ for example), both slopes are positive, but the slope of $g^{-1}$ is greater than that of $f$.
Does it make sense to say $x_{max} = f^{-1}(y_{max})$ or $x_{max} = g(y_{max})$? ($x_{max}$ would be reached earlier in the second case.)
Considering that $y$ is bound by $y_{max}$, what can be said about the possible maximum value of $x$ that could be reached?
As far as I understand, it makes sense to do a linear regression of the form $y=f(x)$ when $x$ is the independent variable and $y$ is the dependent variable. However, in this context, I'm not sure whether it makes sense to consider that $x$ is independent and $y$ is dependent.
Would a total least square regression be more appropriate? Are there other methods to determine which values of $x_{max}$ can be reached (and with which likelihood)?
(If this matters, $x$ and $y$ don't seem to follow a normal distribution, as more attempts have been made to try to reach higher values of $x$.)