Indeed. But people's income often increases over time and many Amex Card-members have had their cards for many years. also some people may have fudged their stated income (yes shock, horror I know...)
Many will also have other forms of income. ie I gain share dividends, but I leave this off my CC applications as I am above the income required and some places will then ask you to substantiate that income despite being well above it.
In addition if say Amex wanted to target people for say its Centurion Card it may well look at such spend patterns, along with other spend.
DISCLAIMER: The article is a USA one and I am not familiar with how their tax system works and how tax is paid.
However how much they would look at that particular source of data I have no idea. But they do mine BigData from a number of sources.
A year ago they had 800 data scientists, and so probably have even more now.
“Big Data is a mindset” concludes Gupta, “we see Big Data as a fundamental driver of the future of American Express”. This is the promise and the ambition of Big Data.
Forbes Welcome
BigData is clearly mined by the banks and Amex including their credit card teams. This can be taken advantage of. ie I have not received Coles Mastercard GC offers in the past apart from the generic ones and so I have just started buying some now with the hope that I will be included in future targeted promotions. If I am it will be dueto the use of BigData.