Base N will allow you to specify a sample size for a Virtual Question (VQ) that is different than the total respondents for a survey. It affects the summary percentages by working as filter, only counting respondents who match the question you enter. For example if you have skip, show if or group logic in your survey and Q5 was only answered by 200 respondents and not the total 400 respondents collected you can adjust the Base N of a VQ to match that sub-population.
After you set up your virtual question and before you calculate the chart click on Base N to enter the question (or questions) number that match subset of respondents you want to target.
A common use case for Base N would be analyzing monadic legs, when you want to calculate based only on the set of respondents who were exposed to a monadic leg instead of the total survey respondents. However, this feature can be applied for anytime you want to focus on sub-populations within a survey.
Questions about using Base N or other Data Lab or Virtual Questions? Don’t hesitate to reach out!