Here's a gross oversimplification and generalization of the study: He cut open every oil filter he could buy from an aftermarket parts store and compared what he found inside. Can be useful, but . . . Toyota filters were not included in the sample group. Frankly, I've never been so concerned as to ruin a filter by cutting it open - but wouldn't be hard to do - just watch out for metal cuts - one author of a similar study found out by slashing open his hand along with the filter. Have seen Toyotas racking up 300,000 miles and more on stock oil filters, so that was good enough for me.