A/B testing – running simultaneous tests of different versions of a website or app on random sections of an audience to see which performs the best – is one of the most important processes that developers can go through. It challenges your assumptions and can have a major impact on your bottom line.

Dan Siroker is an ex-Googler who went on to oversee A/B testing on Barack Obama’s 2008 presidential campaign website. Through testing different versions of the homepage, A/B testing led to the campaign raising $57 million more than it would have done if the team had based their design solely on their assumptions of what would be popular.

Now Siroker runs Optimizely, a startup offering software to help with A/B testing. At The Next Web Conference Europe 2013, he took us through some of the many lessons learned from A/B testing both on the Obama campaign and by Optimizely’s customers.

Catch up with all our coverage from The Next Web Conference Europe 2013.