Ask HN: How to find sparse data domains?

I'm trying to make a complete list of domains with very less data available, either due to sensitivity concerns that can arise due to public release or lack of structured/labeled data and such. Health and finance have some segments where data isn't available for public use and but I've not yet made any comprehensive list with data that's of primary importance in those fields. I'm interested to see if there are any reports or research focusing on this issue of lack or availability of data across all the domains.