https://www.forbes.com/sites/greatspeculations/2019/06/11/how-has-the-u-s-online-advertising-market-grown-and-whats-the-forecast-over-the-next-5-years/#567b6cf76607

https://adage.com/article/print-edition/ad-age-imagines-a-world-ads/300552

https://www.mediapost.com/publications/article/275705/if-there-were-no-ads-how-much-would-you-pay.html

https://www.adassoc.org.uk/credos/does-advertising-grow-markets/

https://www.cjr.org/tow_center_reports/native-ads.php