How Facebook’s Bid Cap influenced overall results Experiment ID: #10909

Buckner International

Buckner International is a global ministry dedicated to the transformation and restoration of the lives we serve. We are a Christ-centered organization that delivers redemptive ministry to the most vulnerable from the beginning to the ending of life.

Experiment Summary

Timeframe: 1/7/2019 - 1/10/2019

Buckner International had recently experienced two significant lifts to their 7 Scriptures email acquisition offer that had resulted in a boost to instant donor conversion. The resulting boost also reduced the cost per donor. It fluctuated by day but were were seeing some days with a cost per donor acquired of $50 or less. However, it was unpredictable.

In an effort to control the costs, we decided to test out the setting a cap on our bid of $50. This would allow us to potentially limit our costs, assuming the strategy worked.

Research Question

Will setting a bid cap of $50 decrease our costs per donor acquisition?


C: No Bid Cap
T1: Bid Cap of $50


Treatment Name Conv. Rate Relative Difference Confidence
C: No Bid Cap 0.03%
T1: Bid Cap of $50 0.00% -100.0% 84.3%

This experiment has a required sample size of 28,182 in order to be valid. Unfortunately, the required sample size was not met and a level of confidence above 95% was not met so the experiment results are not valid.

Key Learnings

We were unable to validate this experiment because, with the low bid cap of $50, Facebook was not able to show our ads to enough audience to receive a conversion. While we were getting conversions for $50 or less without the cap, limited the spend to this low dollar resulted in Facebook not being able to show the offer enough. Without the audience exposure, we were not able to acquire any donors. While we did save ad spend, we sacrificed results which is not worth the trade off.

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Experiment Documented by...

Kevin Peters

Kevin is the Chief Technology Officer at NextAfter. If you have any questions about this experiment or would like additional details not discussed above, please feel free to contact them directly.