Threshold models work by modeling a discrete character as underlain by some other, unobserved, continuous trait (called the liability). If the liability crosses a certain threshold value, then the dis...Threshold models work by modeling a discrete character as underlain by some other, unobserved, continuous trait (called the liability). If the liability crosses a certain threshold value, then the discrete state changes. More specifically, we can consider a single trait, y, with two states, 0 and 1, which is in turn determined by some underlying continuous variable, x, called the liability. If x is greater than the threshold, t, then y is 1; otherwise, y is 0.
