The Google AdWords blog has posted an interesting piece about the effect of the pre-Christmas period on PPC advertisers. Not surprisingly during this competitive period, clicks and often costs will increase, either from increased bidding or higher than usual activity on the most common - and therefore most costly - search terms. However, as Google says, it can also be reflected in higher conversion rates, although this is something advertisers need to keep a close eye on what is happening and what competitors are doing, otherwise it can be an expensive campaign!

The most interesting aspect of this post, however, is the graph used as an illustration of the main points being discussed. This shows overall data from the 2006 pre-Christmas period from advertisers who were using conversion tracking (and mostly from ones based in the US) and it displays the trend of the median CPC (cost per click), the median conversion rate, and the median CPA (cost per acquisition).

The blog article includes an explanation of the trends seen on the graph so it's not necessary to repeat it here, but do take a look at the graph and see how the CPA reacts to the other metrics during the period.