Why have measures of earnings quality changed over time?

The properties of earnings have changed dramatically over the past 40 years. Prior studies interpret this trend as a decline in earnings quality but disagree on whether it results from changes in the real economy or changes in accounting standards. I find that each new cohort of listed firms exhibits lower earnings quality than its predecessors, mainly because of higher intangible intensity. I conclude that the trend of decline in earnings quality is due more to changes in the sample of firms than to changes in GAAP or in the earnings quality of previously listed firms.