Estimating visitor traffic from PPC campaign

Can this be done with any accuracy?

[fom2001uk]

Someone has asked me to give them a forecast of the traffic they might expect from a PPC campaign. Now I know that the engines will give you numbers on keyword searches done previously, but I would be inclined to treat those figures with a pinch of salt.

Does anyone think differently?

[Travoli]

There are so many variables that this can be difficult.

Title and description copy have a lot to do with clickthroughs. Competitive terms fluctuate constantly.

We have some terms with a .5% CTR and some with a 27% CTR.

My advice is to start small with some targeted 3-4 keyword phrases, bid as high as is profitable, track your results, and then adjust your campaign according to your budget and ROI.