tedster - 6:51 pm on Apr 16, 2013 (gmt 0)
First, I assume those dates should be 2012. Is that correct?
Next, small traffic changes such as 5% down or up can be extremely challenging to analyze. For example, it can be that rankings changed for just a few locations. It can be that the Google Suggestions drop down changed. It can be that other sites were given a promotion for some reason and your rankings drop was a side effect. These factors are almost impossible to nail down.
If you can zero in on specific keywords whose traffic changed, then you might have something a bit more actionable. If you find a keyword that shows a major traffic drop, then that could be a keyword-specific penalty and you could investigate further. One keyword's major drop could generate an overall 5% drop.