I think the 100% is when the data shows the recession is occurring i.e. if a recession is occurring now, then the chances of one occurring in the next 3 months

I think the 100% is when the data shows the recession is occurring i.e. if a recession is occurring now, then the chances of one occurring in the next 3 months are clearly 1 (I get your point however...it is odd). There are other factors in the model aside from the ones with charts. The model isn't in a textbook because predicting the economy is nothing to do with economics as it is taught at universities. Economists use complex structural models because they are fun to teach and create barriers to entry. This is why DSGE models are so popular in universities, govt, and central banks but barely used anywhere else. If you want to forecast the business cycle, you just need linear regression. You can't ever be 100% (unless a recession is already occurring) because the economy is always changing but basic models are pretty accurate (the BIS has done quite a bit on this recently - https://www.bis.org/publ/work818.htm https://www.bis.org/publ/work818.htm - funnily enough, the term spread isn't the be all...but economists have a big problem with including things like credit.