What criteria determine whether a Stack Exchange site should carry ads?

Question

This is a question about paid advertising, not cross-site promotion or community ads.

The Stack Exchange Media Kit has a list of sites that accept advertising: besides the SO, SU, SF, they are Android, Arqade, Ask Different, Ask Ubuntu, DBA, Drupal, Game Development, Programmers, Information Security, SharePoint, Unix/Linux, Web Applications, and WordPress.

By what criteria where these sites chosen? It can't be just their traffic: several sites have higher traffic than those listed above, yet have no ads (ELU, Mathematics, Seasoned Advice, Home Improvement, TeX, Electrical Engineering, Graphic Design, Travel, ...).

Has it been decided to limit advertising to technology sites, with all other categories being free riders? But even then: EE, GIS, and Salesforce are within the technology group, with traffic greater than Drupal's, yet with no ads.

Answer 1

Great question! Below is a quick answer for you.

1/ Tech sites
We chose technology sites (ruling out Cooking, Bicycles, Home Improvement, etc.) because we felt they could be a logical extension for existing advertisers. We work hard to ensure the relevance of an advertiser (and campaign, and creative) before they run a campaign on SO; by choosing sites with an overlapping audience, there is a reasonable likelihood of overlapping advertisers. Plus, existing advertisers already understand the unique way we run ad campaigns at this company, so there is less of the initial friction.

2/ Traffic
There wasn't a 'critical traffic metric' that influenced our decision to select one site over another. More important was a site being active enough where introducing advertising would not be a distraction to a young and/or growing community.

3/ Existing advertiser interest
This falls under 1/ a bit, and it's pretty self-explanatory but if one of our existing advertisers expressed interest in advertising on one site, that added some weight in our opinion.

4/ Sales staff bandwith
Finally, we had to cap it somewhere. We definitely could open up more sites-- and probably will in the future-- but we thought this would be a good first step.

I hope this clears things up a bit!

Answer 2

This is definitely an interesting question. It's probably combination of many things right from unique visitors, page views, target audience, technology sectors, etc.

There is hardly any data available as for the paid advertising criteria goes, but I found an article on Adzerk (Stack Exchange's Ad serving platform). Here is an excerpt from that article: (emphasis mine)

Also, since Stack Exchange sold their ad inventory based on product keywords, they needed a system that could target combinations of keywords (excluding competitors) which could later be broken out in reports. It was difficult for them to judge how much of their inventory was available for a given keyword, which complicated their sales process.

So, based on the above excerpt, we can definitely say that Stack Exchange has built a product keywords database (or tags) from analyzing the data e.g. search volume, keyword traffic, most tagged, etc. across its network sites. And, most likely (I'm guessing here) some of the product keywords/tags may be coming from these new sites (apart from S[OFU]) that are accepting advertising.