What principles does conversion rate optimization share with direct response marketing?

Context: Online conversion rate optimization was born out of the need of e-commerce marketers to improve their website's performance in the aftermath of the dot-com bubble, when technology companies started to be more aware about their spending, investing more in website analytics. After the burst, with website creation being more accessible, tons of pages with bad user experience were created. As competition grew on the web during the early 2000s, website analysis tools became available, and awareness of website usability grew, internet marketers were prompted to produce measurables for their tactics and improve their website's user experience.

In 2004, new tools enabled internet marketers to experiment with website design and content variations to determine which layouts, copy text, offers, and images perform best. Testing started to be more accessible and known. This form of optimization accelerated in 2007 with the introduction of the free tool Google Website Optimizer. Today, optimization and conversion are key aspects of many digital marketing campaigns. A research study conducted among internet marketers in 2017, for example, showed that 50% of respondents thought that CRO was "crucial to their overall digital marketing strategy".

Conversion rate optimization shares many principles with direct response marketing – a marketing approach that emphasizes tracking, testing, and on-going improvement. Direct marketing was popularized in the early twentieth century and supported by the formation of industry groups such as the Direct Marketing Association, which was formed in 1917 and later named Data & Marketing Association and acquired by the Association of National Advertisers following the announcement on May 31, 2018.

Like modern day conversion rate optimization, direct response marketers also practice A/B split-testing, response tracking, and audience testing to optimize mail, radio, and print campaigns.

Answer: They are both marketing approaches that emphasize tracking, testing, and on-going improvement. Direct response marketers also practice A/B split-testing, response tracking, and audience testing to optimize mail, radio, and print campaigns.