As savvy webmasters and marketers installed Google Analytics and maintained the conversion counter, they discovered that the numbers (conversions and sales value) the conversion counter reported looked different (often very different) than Google Analytics numbers.   There are a few reasons for this (none of which are really explained by Google’s help entry on the topic):

1. Date-of-click vs. Date-of-sale - Google conversion counter attributes a conversion (and sales value)  to the date of when a customer clicked on the ad.  Google Analytics attributes the transaction to the date of the sale.   For example, if I clicked on an Adwords ad on May 1, but then came back to the site through anyother means besides clicking on the ad again (ex. bookmark, direct) and purchased on May 15, Google conversion counter would attribute the conversion to May 1.  Google  Analytics would attribute the sale to the date of the sale – in this case, May 15.  (Note:  This gets tricky when you are looking at visitors who click at the end of one month, and purchase in another.  See Adwords Tip: Run Look back reports when using conversion counter)
2. Separate Cookies - GCC and GA are on two separate systems (GA is built on the old Urchin platform).  With cookies coming from separate servers, there is bound to be cookies that may be dropped by one system and not the other.  Users may also be blocking one and not the other as well.
3. Improper/Missing Page Tagging – Proper installation of the tracking codes on landing and receipt pages is critical with any tracking system.  Nine times out of ten, improper or missing code installation is the root of reporting issues.  Make sure you follow the instructions provided for both codes and TEST, TEST, TEST.  The first thing to check when you see no data coming in – are the pages still tagged with the codes.
4. Improper URL tagging – Google has made is very simple for Adwords advertisers to link their campaigns into an GA profile.  Using the auto-tagging feature, it’s the click of a button and your campaign data is feed into GA.  Still, there are those who manual tag Adwords destination URLs, and simple tagging errors can reek havoc on your Analytics reporting.  Again, test often, especially if your site is frequently updating pages/code.

We attended the GA Conversion Universiy last week and it was discussed why Google Analytics time on site numbers have jumped.

Google’s explanation is that Google Analytics is no longer counting visitors who bounce in their TOS calculation. They weren’t sure when the change took effect (they thought end of July). The Google folks agreed it should have been announced.

I think most agreed that this was a better way of measuring time on site becaues the way it was explained is that TOS is calculated is looking at the time between one page is called to the next. With those that hit the homepage and leave, they were getting zero values, bringin the TOS down – even if they spent a couple of minutes looking at your homepage, then left.