You either did not understand what I advocate or you do not understand speculation.

The difference between investment and speculation is as follows: investors purchase a claim on future cashflows and seek to make returns by receiving those cashflows. Speculators purchase just about anything and seek to make returns by hoping it goes up in price so they can sell it more dearly later.

retail day traders who spend their time speculating fare much worse in the marketplace than those who stay invested and do not try to make such predictions.

I'm not sure what makes you think any part of my post suggests short term trading. I think buy-and-hold index investing is a very good strategy, and I do not think that one should expect to beat it with short term trading. I do however think that buy-and-hold will deliver lower average annual returns over the next 30 years than it did on average in the last 50-100 years.

Further, it's not logical to choose "1 of 20" variables and make investment decisions based on that variable when you don't know the impact that it will have on the assets you are invested in.

I do know the impact that 1% lower population growth per year will have on GDP: if all other inputs grow at the same rate that they generally grew in the past, it will make GDP grow 1% less quickly per year. The fact that there are many other unknowns doesn't mean we throw out whatever useful information we do have. Imagine if you did that in any other context: i.e. "The Yankees are playing the Mets in Yankee stadium tomorrow, with the Yankees' best pitcher facing the Mets' worst pitcher. But of course we don't know with certainty who will win the game, so I guess it's just automatically 50/50."