I checked the http://www.alexa.com/ site and found that I could compare the two sites over several periods of time. Start at http://www.alexa.com/data/details/traffic_details/ancestry.com.
Here is the comparison for the last month for "Reach" - that is unique visitors per million Internet users per day:
Here is the comparison for Page Views.
The first graph shows that the Rootsweb Reach (unique visitors per day) went down simultaneously with the Ancestry Reach going up from March 20 to March 21 - pretty much a 1 for 1 variation of magnitude 40 to 50 per million. But the number of page views for both sites went down from March 20 to March 21.
We can see from the first graph that Rootsweb.com had more unique visitors than Ancestry.com over the last month, which matches the Quantcast numbers I posted several weeks ago noting Rootsweb was #1 in US Reach. But Ancestry had many more page views than Rootsweb, which increased their Rank calculated by Alexa.
The www.Ancestry.com statistics for the last week indicates that -
* 0.021% of Internet users visited this site. That's 1 in 4,760 worldwide Internet users, approximately.
* Rank of 3,267 of all web sites worldwide (combined measure of page views and visitors).
* 14.1 page views per user per day
* 55.2% of all Ancestry users come from the USA, with a rank of 582 in the USA
* 3.8% from United Kingdom, 3.0% from Canada, 2.5% from Puerto Rico, 2.2% from Chile, etc.
The www.rootsweb.com statistics for the last week indicates that -
* 0.026% of Internet users visited this site. That's 1 in 3,850 worldwide Internet users, approximately.
* Rank of 5,638 of all web sites worldwide (combined measure of page views and visitors)
* 3.2 page views per user per day
* 41.2% of all Ancestry users come from the USA, with a rank of 582 in the USA
* 5.6% from United Kingdom, 5.0% from Canada, 3.2% from Dominican Republic, 2.6% from Australia, etc.
There is more data on this site for every web site. Go experiment on this site - it's free and interesting.
I will post several more comparisons in the next week to show how different types of web sites have changed in traffic.
I do have several observations about the data:
* The 0.021% reach for ancestry.com (1 in approximately 4,760 worldwide Internet visitors) is nowhere near the approximately 20% of US residents who claim to be interested in genealogy research. Even if the reach for ALL genealogy web sites was 2% I would be surprised - it's probably more in the 0.2% to 0.5% range (we could find out by adding up all of the Reach numbers one at a time, I guess!). A 0.5% reach would be about 1.5 million people in the US (300 million population).
* The change in domain name for the main Rootsweb page has worked - Ancestry gained more reach and rank, Rootsweb less. As more Rootsweb pages are transferred to the Ancestry domain name, we will see the Rootsweb numbers continue to go down. A factor in this will be the migration of USGenWeb pages off the Rootsweb domain. We'll have to re-visit this in a month or so when the migration is complete.
* 55% of all Ancestry users are in the USA - I'm surprised that this number is that low. I'm even more surprised that 41% of the Rootsweb users were from the USA - my guess would have been something like 80% for both of them.