April 26, 2019

Anyone with experience with FB A/B tests?

Hi - hope someone could help me out.
Before I created my A/B tests on Facebook, I used Optimizely's sample size calculator and found I needed a sample size of let's say 5,000 per variation to reach 95% statistical significance. While I was setting up my campaigns, Facebook said the potential reach will be 100,000 so I thought I was safe.
However, my campaign, which is 2 weeks, is about to end and I only reached <300 per variation (which is well below the sample size needed to reach stat sig).
What am I doing wrong & how could I avoid this next time? Thanks in advance for your help.