English: This is a simple two person signalling model. It is optimal for the higher ability person to obtain the credential (the observable signal) but not for the lower ability individual. The structure is as follows:

There are two individuals with differing ability (productivity) levels. The premise for the model is that a person of high ability (h) has a lower cost for obtaining a given level of education than does a person of lower ability (l). Cost can be in terms of monetary, tuition, or psychological, stress incurred to obtain the credential.

W_o is the expected wage for an education level less than S^*, W^* is the expected wage for an education level equal or greater than S^*

Thus, if both individuals act rationally it is optimal for person h to obtain S^* but not for person l.

In equilibrium, in order for the signalling model to hold, the employer must recognize the signal and pay the corresponding wage. One can see that the cost/benefit structure for a signal to be effective must fall within certain bounds or else the system will fail.

I drew this myself in mspaint, do whatever you want with it, I don't care.