Google AdWords vs Analytics conversion data reports

I've noticed that there's usually a difference between the number of conversion reported by Google AdWords and the equivalent count in Google Analytics, despite the two accounts being fully integrated.

I've a theory to explain it as follows:

Google AdWords, in an attempt to maximise its apparent value, uses cookies to track conversions, meaning that it is able to attribute a sale to AdWords for several weeks to come, even if the customer finally returns via another channel.

For example, it's common for the conversion count for last month to continue to increase slowly for several weeks after. This can only be because people who first clicked on an AdWords ad last month have just returned to buy.

My understanding of Google Analytics however, is that it's set to 'last source wins' as standard i.e. if a customer first visits our site via Google AdWords, but then later returns via the natural listings, Google Analytics will attribute the sale to SEO, rather than to the PPC campaigns.

This would explain why AdWords reports more conversions than Google Analytics, despite similarities in their underlying technology, but are my assumptions correct?

Can any analytics specialists please confirm that this is how the tracking of these Google products works?

Thanks,

Anthony Sharot

SEOCompany Market Appeal

I'd also be very interested to know if this is the case. Analytics definitely uses "last source wins" (and this is the number one flaw in the product IMHO) but Adwords could well be using cookies - if so, what is the duration?

The descrepancies are even greater if you consider what happens if you advertise off-line, or do email campaigns to your customer base.

Here's my findings http://www.e-consultancy.com/forum/110690-google-analytics-do-you-understand-your-numbers.html