Funnel Visualization in Google Analytics

[Unity]

Hello.

I have a question about funnel visualization in Google Analytics where there is an eCommerce goal (i.e. add to cart, shipping, purchase) with the first step being mandatory.

Issue:
The amount of completed purchases reported in GA doesn't match the actual transaction figure via the eCommerce platform.

Question:
I was wondering if anyone knows why this occurs? I have a few ideas on why  however I haven't been able to locate any supporting evidence. So I was hoping to generate a few ideas from the SEOMoz community to help me investigate further.

Any ideas welcome!

Much thanks,
Davinia

[Unity]

Thanks Chris, I'll look into this avenue.

[cogbox]

It's an interesting question. I see the same problem frequently with leads.

Part of the problem may lie in the tracking method -- that the transactions aren't actually recorded at the same time.

1. Your server completes and records the transaction, and composes a receipt page (this is where your ecommerce system records the transaction)

2. The browser client executes the google analytics JS on the receipt page (this is where your transaction is recorded in analytics).

There's a Q&A on the Analytics support site that provides some possible answers here.  <--weak anchor text btw