VBA code and formulae allowing statistical analysis in MS Excel without add-ons.

1. If test conditions* are met, do a pooled Z test comparing 2 proportions.
2. If test conditions are met and significant difference is found, return the proportion difference.
3. If test conditions are not met, or there is no significant difference, do not return anything.

=ABTest_Proportions(n1,y1,n2,y2)

1. n1*p1 > 5
2. n1*(1 - p1) > 5
3. n2 * p2 > 5
4. n2(1 - p2) > 5

Where:

1. n1 - sample size of group 1
2. n2 - sample size of group 2
3. y1 - count of instances of success in group 1
4. y2 - count of instances of success in group 2
5. p1 - proportion of group 1: y1/n1
6. p2 - proportion of group 2: y2/n2