In fact, knowing just four random pieces of information was enough to reidentify 90 percent of the shoppers as unique individuals and to uncover their records, researchers calculated.
https://bits.blogs.nytimes.com/2015/01/29/with-a-few-bits-of...
Contrast this with trying to identify a single individual in a population with no other information about them. It would take about 33 bits if we knew absolutely nothing about her, given log_2(7,280,000,000) = 32.7. But we know she’s American, so we can cut our search space down to 322,000,000. That leaves us with 28 bits. We also know she’s a woman, so we can cut our search space down by 50%. Now we have 27 bits to go. I can virtually guarantee you an analysis of anonymous donation patterns will not meaningfully cut down the search space beyond a few more bits, and that’s exceptionally non-random data. The more useful information is knowing that she resides in New Hampshire, but that still only brings us down to approximately 20 bits.