Noun as modifier—singular or plural?

Question

Which one is correct?

• statistical models for process monitoring

• Statistical models for processes monitoring.

Answer 1

I'm sure I've seen this question before.

Anyway, the common usage is to put the noun in singular when used as modifier:

• Statistical models for process monitoring

(there's no verb here; "process" acts an adjective, modifying the gerund"modeling".)

The alternative would be

• Statistical models for monitoring processes

(Here, "processes" is the object of "modeling". One could argue that there's no verb here either; it still behaves like a gerund)