Currently, about 7.4% of respondents have left our NPS question blank. 50% of those respondents were using an iPhone, and the other half appear to be using very narrow desktop browsers. About 40% of these respondents are college students, so it's fair to say they're a younger demographic who I'd expect to be familiar with navigating mobile websites.
Here's what the NPS question looks like on mobile:
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Not all mobile users are experiencing this problem, and when I've tested the survey on multiple devices with the same characteristics I've been able to select a response without issue. Respondents also always answer several questions following NPS, so the problem can't be survey abandonment. I'm assuming that they find the scale to be confusing, and are simply skipping over it.
Has anyone else noticed this behavior with NPS on mobile platforms? Do you have any suggestions for improving the response rate for this question on mobile devices?