Jim, I don't really know what is going on with regards to approaching this as a formal statistical evaluation. And I have never approached science in that way.
For ENSO, all I am trying to do is apply elementary formulations of fluid dynamics to try to understand what is going on in terms of the apparently erratic oscillation. This approach may be naive but I think it is worth a shot, especially considering that I have found little evidence of anyone trying this path in the literature.
So when I find out right away that a sinusoidal forcing function with the same frequency of the QBO gives a decent correlation, this is the opening to go for. Adding the frequency of the other hypothesized forcing, that of the angular momentum Chandler wobble, only works to improve the agreement. The TSI also has some important contribution to play.
The essential statistical question that remains is to ask whether this correlation is simply a staggering coincidence.
In other words, I have no idea of how to provide a statistical likelihood that this is a realistic behavioral model of the driving physical mechanism behind ENSO.
> "I sort of expected a comparison with Graham Jones's Ludescher et al. R code in the github repo."
This is a good question but I just don't know how to answer it.