Thumbtack has an open-source split testing calculator which makes it very easy to see whether or not results like these are significant or not: http://www.thum

Thumbtack has an open-source split testing calculator which makes it very easy to see whether or not results like these are significant or not: http://www.thumbtack.com/labs/abba/#Sunday=47%2C389&Tuesday=35%2C378&Wednesday=37%2C400&Saturday=25%2C401&Monday=35%2C379&abba%3AintervalConfidenceLevel=0.95&abba%3AuseMultipleTestCorrection=true http://www.thumbtack.com/labs/abba/#Sunday=47%2C389&Tues... If we treat "Sunday" as the baseline and use "votes" as the count of a successful email, it appears that you can say with a somewhat high degree of confidence that Sunday is better than Saturday, but nothing else.