Let’s say that I tell you that if 100% of the population smokes one cigarette a day then the whole population will lose 15 years of life and if no one ever smokes a single day in their life then no years of life will be lost.
What have I predicted? Did I predict 15 years of life will be lost or did I predict 0? Are my numbers completely wrong? That’s the wrong way of thinking about a prediction.
The word “predict” in scientific modeling means a different thing from what you think it means.
A scientific prediction gives scenarios that allow the decision makers to get a flavor of the range of possibilities and what sorts of things will happen on the basis of those. It’s not an attempt to predict the future any more than I am predicting what you will order at my restaurant when I hand you the menu. I can tell you what you’re not going to order, but you have full choice from anything on the menu itself and I can’t force you to pick one, I can just tell you which are smarter and which are dumber.
But now let’s say that the decision makers make a decision and go back to the scientific modeler a month later. Well, now one month’s worth of time has been settled and can’t be changed. Any models of what might happen from here, depending on the choices, are going to have to start from the current position.
If 30% of people have been smoking for the last 20% of the time period that we care about then, no matter what, I can’t get the years of life lost to smoking down to 0. It’s too late. We’re already 20% through and we didn’t maintain the zero smoker result that we were hoping to accomplish. Our range of possibilities will now be smaller - between 3 years of life lost and 15 - and that’s not more accurate a prediction than last time because I was stupid, ignorant, and incapable before, it’s because options have now been taken off the menu and are no longer available.
Now in the case of FiveThirtyEight and their Covid-19 predictions, probably the scientists have improved their models between then and now, to be more accurate. But they’re still not “predicting the future” in the way that you think. They’re giving a range of options that decision makers can choose from and saying where we should expect to land, on the basis of those. If you see the decision makers making good choices, then we won’t land “somewhere in the middle” of the predictions, we’ll land at the bottom end of them, because that’s where we chose to drive. If we land in the middle or at the top, it’s because the decision makers decided to be morons and drive towards more death.
As said, it’s a menu, not a prediction.
We end up inside the bars based on where we’re mentally capable of arriving. It’s not prognostication, it’s our range of options.