Source for statistic I keep reading about PPC budgets

Most companies waste 30% of their budgets on bad keywords

[handsome rob]

I have been looking around at PPC management agencies and several times I've read that most companies waste ~30% of their PPC budget on non-converting keywords.

Where is this figure coming from? I've searched high and low through search engines and research groups like SEMPO and comScore but I can't find any data backing it up. What's more, the companies citing this number don't provide a source.

Can anyone point me in the right direction for this "fact" or a related study? I'd greatly appreciate it.

[shorebreak]

I know of one SEM tool vendor whose ads keep a running estimate of total $$ advertisers waste on PPC, due supposedly to poor SEM management. That's just their guess, though, and has no relation to fact. That said, the tab's currently at ~$5B, which would work out to 20%+ of total ppc spend.

Generally speaking, though, I would wholeheartedly concur from experience that 30%+ inefficiencies exist in more campaigns than not. I don't, however, have any published figured to share with you.