The base line is the original version of your web page that you are optimising which you use as your benchmark conversion rate to compare against other variants of the page.
In this A/Bn test of the Cheekybingo.com registration form the base line conversion rate was 64.85% (the default). However, the conversion rate for variant 1 was 67.15%. As a result the variant 1 was the winner with an uplift of around 3.5%. This resulted in additional revenues from first-time deposits of around £41,000 per annum.
Conversion marketing – Glossary of Conversion Marketing.
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