Flawed Concept of CPC Media Planning

I am aware my comments below are a big over-simplification but here goes - We are a metric led business or to be more accurate - we advise our clients based on a set of metrics that we hold or have access to on their behalf. However - this very puritanical form of measurement and evaluation of campaign success or media performance cannot and should not exist in isolation. I was debating with Kork earlier who works with a product agency on one of our accounts who wants to select media for next campaign based on pure CPC basis (or to be fair a CPA) basis as they would do a consumer campaign. All sounds good.... The big signifcant difference between candidate attraction campaigns and selling product campaigns is that the ideal response to a single job ad (or any number of jobs) is 1 (or 1 per job). That 1 being the ideal candidate. All further response has a cost (a sift, a phone interview etc) however minimal that would be. For purpose of this i will ignore building talent pool/database etc. The ideal response for a product/service sales campaign is as many as possible. Somehow qualitative data or insight has to be introduced and planning decisions weighted accordingly In summary - metrics, CPC/CPA are critical measures but in isolation can lead you down a very misleading road.