Qualitative surveys ask open-ended questions to find out more, sometimes in preparation for doing quantitative surveys. Test surveys to eliminate problems.| Nielsen Norman Group
Open-ended questions result in deeper insights. Closed questions provide clarification and detail, but no unexpected insights.| Nielsen Norman Group
Calculating the sample size required for an AB test prior to starting prevents us from running the test for a smaller sample size, thus having an “underpowered” test.| Invesp - Conversion Rate Optimization Blog