This Inside Higher Ed story talks about the difference between certificates and degrees, suggesting that certificates are additional rungs on the metaphorical education ladder. (Whew, that’s an interesting metaphor that I don’t have time to deal with!)
Where it gets really interesting is the second part of the story, which shows that the certificate holders who get the biggest pay bump as a result of their new credential are men. This statistic is certainly also affected by the concentration of men with certificates in higher-paying fields (like computing) and women with certificates in lower-paying care professions (nursing, for example). This seems like an interesting incarnation of the gender wage gap, and I’m interested to see what the promised 2014 census report has to say about it.