Local SERPs Question - Phone Call or Click?

[Dave_Eddy]

I have a client who recently experienced a boost in local organic rankings. They were appearing towards the bottom of the local (maps) results (with their phone number & address listed) for their main target keywords. After this ranking boost, they are now positioned higher in the SERPs, in the traditional organic section.

It seems as though this boost in rankings has actually caused a slight DECREASE in organic search traffic to their website. My theory is that when they were listed in the Google+ Local section of Google, some people must have been calling directly from the SERPs instead of actually clicking through to their website. Due to the issues involved with organic call tracking, it's obviously difficult to measure the actual impact of strong Google+ Local rankings.

So, I'm on a mission to find some reliable data on this. For my own peace of mind and that of my client.

Does anybody know of any research conducted that analyses the % of local searches that result in a phone call directly from the local SERPs without actually clicking through to a business' website or Google+ page?

In know this is a tricky one (and probably harder to ascertain on desktop than mobile) but any advice would be much appreciated.

Thanks!