This is a very good question and would seemingly be implicated in a critical view of the reporting methodology. I have been impressed with the work the NYT data

This is a very good question and would seemingly be implicated in a critical view of the reporting methodology. I have been impressed with the work the NYT data team shows on their github (or whatever). It looks like the economist has an account: https://github.com/economist-data-team https://github.com/economist-data-team but in a few minutes searching around couldn't find any links to data sources. There was a footer mentioning that you could read more on the marriage special report, but I encountered a paywall :)