How does A/B testing for Overlay campaigns work?

1) Create an Overlay campaign, select at least 2 Ads

2) A/B testing starts automatically – each Ad is shown at least 500 times, and the most effective Ad remains active, others are deactivated. You can see statistics about each Ad when you click on campaign name in Overlays section.

3) If later with new impressions the active Ad starts to perform worse than others, then the most effective Ad is activated, others – disabled. So A/B testing process is running all the time. 

How does the system decide, which is the best performing Ad?

a) If there is any data available about Orders (conversions), then Ads are compared based on Conversion Rate.

b) If there is no conversion data, but campaign collects Leads, then Ads are compared based on Subscribe Rate.

c) And in case there is no data about Conversion or Subscribe Rate, then Ads are compared based on Click-Through Rate (CTR).