Please consider the following two main clauses.

> 
> Both variables have the same range of values. Therefore, a 4:3 aspect ratio has been chosen.
> 
> 
> 

I would like to combine these two main clauses into one sentence containing a main clause and a relative subclause like this:

> 
> Both variables have the same range of values why a 4:3 aspect ratio has been chosen.
> 
> 
> 

Is this grammatically correct? I could not find an authoritive answer on the web. While [this page](https://owl.english.purdue.edu/owl/resource/645/01/) mentions `why` as a relative pronoun, it does not give an example. In contrast, [Wikipedia](http://en.wikipedia.org/wiki/Relative_pronoun) does not mention it as relative pronoun at all.

If my second sentence is grammatically incorrect, could you suggest a way to rephrase it?