Is the physical impact / effect necessarily the independent variable / dependent variable of the regression model A regression analysis (RA) is often explained as follows:
"...Regressions analyses are statistical methods, by which you can calculate, whether an independent variable (IV) impacts a dependent variable (DV). So, in contrary to a correlation it is possible to evaluate causal effects and not only relations. Within RAs the IV is also called predictor, cause or regressor, whereas the DV is often called target variable, effect or regressand..."
What now is confusing me, is the equating of the terms independent variable and cause, or of the terms dependent variable and effect, respectively, - when reflecting what is the calculation direction of my regression model and what is the natural or physical impact-effect direction.
Lets take an example:
At a certain date we measure the water depth at several points (at the inclined ground) of a large, clear lake. For these points at the same date we also have the reflection values from satellite-borne imagary. Say we are interested in the reflection of the blue band. (Normally, for clear water we would assume a negativ correlation, i.e. blue reflection decreases while depth is increasing.)
Now we want to know whether we can predict depth by the blue band reflection values.
Now, in a regression model depth is the DV, and reflection is the IV, as the input is the reflection and the output is depth. Thus, if equalizing the terms IV and cause (or vice versa DV and effect), reflections values would impact water depth. But from a physical impact-effect point of view it is the complete opposite: water depth causes the measured reflection value (but reflection does not cause depth).
May anybody resolve this contradiction or help me with a link to an according post?
Or in other words: Is it allowed to use a regression like in the example in which the calculation direction goes the opposite of the 'physical' impact-effect direction?
Might be a quite basic question. However, thanks in advance


Is the physical impact / effect necessarily the independent variable / dependent variable of the regression model

NO
In fact, we can use the present to predict the past. It might be more interesting to ask how much money one can expect to make if one goes to additional school (college vs high school, master's vs bachelor's, etc), and we might consider the additional education to cause employers to offer higher salaries. However, if we know salaries, we can predict amount of education, and I do not see much of an argument that present-day salary causes past education.
(Or we can use evidence we see today to predict what caused the dinosaurs do go extinct. Or we can use evidence we see today to predict how Venus developed such a hostile environment. Or we can use evidence we see today to predict the origins of the Universe...but does the Cosmic Background Radiation cause the Big Bang?)
This is one of the reasons why correlation does not imply causation.
