But the real question should be: why doesn't de-identification work and how to make it work. How much health data is required to distinguish a specific individ

But the real question should be: why doesn't de-identification work and how to make it work. How much health data is required to distinguish a specific individual even without any "identifying" information? Surely there must be many people with unique combinations of conditions and treatments. If that is so then a data set that includes those people could only ever be pseudonymous, not truly anonymous. What other data sets might then be combined with the health data to match a pseudonymous record with an identifiable person? Payment records? Travel records? Time off work? Insurance claims? I don't know much about how the US healthcare system works, but maybe before asking how to make de-identification of health data work we should be asking whether it could ever work effectively at all.