I only took intro biostats and I dont think we even covered bivariate/multivariate.

So this is what I learned from the net and guessing. Please correct me if I am wrong.

Bivariate is a special case of multivariate.

Multivariate is used to remove confounders (variables).

P values are usually set at </= to 0.05 but the authors here arbitrarily chose 0.10.

They used bivariate to test which variables are significant so that they can have a more robust model when running only those significant variables in the multivariate model?

I guess I just don't see why they need the redundancy.