73 percent of StackExchange users from StackOverflow

StackExchange is a group of Q&A sites created by StackOverflow (SO).

But exactly which part of the new StackExchange Q&A sites are new users and which part of are shared from StackOverflow?

I mined the November 2010 data dump again and came up with some interesting stats.

To figure out the common percentage between StackOverflow and other sites, I created lists of in memory users for each site, and then figured out which users had the same email hash. A user across sites with the same email hash can be considered the same user.

I knew before doing this analysis that the percentage of common users to StackExchange users would be high because of the relative size of the StackOverflow community. I do fully expect for this 73% to decrease for future data dumps though and it will be interesting to re-run these stats and compare when the next data dump comes out.

Here are the statistics per site:

• Cooking: 2630 of 3155 in common (83.36%)
• Game Development: 2497 of 2938 in common (84.99%)
• Gaming: 3813 of 4418 in common (86.31%)
• Mathematics: 2162 of 2965 in common (72.92%)
• Photography: 1659 of 1916 in common (86.59%)
• Server Fault: 28770 of 38434 in common (74.86%)
• StackApps: 3656 of 3874 in common (94.37%)
• Statistical Analysis: 1298 of 1728 in common (75.12%)
• Super User: 31897 of 49157 in common (64.89%)
• Ubuntu: 3245 of 5090 in common (63.75%)
• WebApplications: 5575 of 6223 in common (89.59%)
• WebMasters: 2612 of 2820 in common (92.62%)

Total: 73.19% in common, 26.81% distinct

Of particular interest are the sites with a very high common percentage and some overlapping questions like the WebMasters StackExchange site.

Update:

What percentage of SO users come from the other sites? I checked the registration dates and a surprising 5% of SO accounts come from the other sites. This doesn’t change the result much above though. Almost all of these 5% of distinct accounts come from Ask Ubuntu, Super User, and Server Fault.