How to randomly allocate donors to your experiment groups

Random allocation is central to the scientific method. This ensures there are no underlying differences between our groups that will bias our result before we even start running the experiment. For instance, if your Control group is full of 80 year olds and your Test group is full of 20 year olds, you may conclude that an intervention worked when it was in fact due to the make-up of the groups. This is an "unfair" test. 

To fairly allocate constituents, use a method for generating random numbers. Here is a guide to doing so in Excel. 

1. Export your campaign list to Excel, you should include every "Constituent ID" that will be in the experiment.
   
2. Create two new columns, "Random Number" and "Experiment Group"
3. Apply the following formula to every cell in the Random Number column =RAND()
   
   
4. Sort the entire table by the column, Random Number.
   
5. In the Experimental Group Column, assign the first 50% of your campaign list to group "Control" and the second 50% of the list to the group "Test" (For a campaign of size 1000, there should be 500 in each group).
   
6. Verify the random allocation is successful by counting how many constituent records in each group. If possible, also confirm that each group has the same age, gift size or summary metric you have available.
7. Export this data to a safe place, which you can return to at the end of the experiment