Dr. Seamus McGuinness:

I will explain what we mean by productivity in this context. If there is a graduate in a non-graduate job that requires the leaving certificate, and the guy beside him is doing the same job and he has the leaving certificate, we would expect that the graduate would earn slightly more than the guy beside him who is doing the same job and has the leaving certificate. He will never earn as much as a graduate in a graduate job because the job itself puts a ceiling on how productive that worker can be and therefore the wages he can earn.