The experiment was intended to point to the way that online presentation can affect how investors choose or manage their retirement accounts, and highlight the need to be sure that that presentation is designed to elicit the best possible outcome. The results were striking.

Although the group given the four-line screen was also given a highlighted link to click if they wanted to allocate among more than four funds, only 10 percent of respondents clicked that link, Benartzi said.

However, among the group given the eight-line screen, "that number quadrupled. This means that the level of diversification was driven, in large part, by a seemingly minor website specification, almost certainly chosen by someone with little investing expertise."

The same principle, Benartzi said, governs the opening of a retirement account, which was formerly done with pen and paper but now generally must be done online, with hopeful participants attempting to navigate a maze of technical challenges before they even get to the part about choosing contributions and allocations.

Benartzi cited another experiment in online account enrollment.

He said, "After replicating a typical online enrollment procedure, we found that about 40 percent of college-educated subjects admit they are 'not likely' to complete the process by themselves…. One of the main impediments is the creation of a username and password, as people struggle to fulfill the security requirements. If we apply these findings to the real world, it suggests that many users will give up after a few frustrations with a website. Their choice to not enroll is not really a choice, then — it's just a side effect of poor digital design."

Easier-to-complete digital forms exist, he said, such as college loan applications substantially populated automatically by H&R Block tax return information rather than manually. These forms dramatically increased submission by 40 percent, were 33 percent more likely to bring a scholarship and made applicants 25 percent more likely to attend college.

Similarly, changing default settings on retirement plans to show long-term, rather than short-term results, can improve participants' decisions, focusing them more on the long term and less on daily changes.

Benarski said that, considering the prevalence of the digital in everyday life, "it's easy to envision a situation in which fiduciaries would be required to consider and measure online participant behavior as part of their duties."

Considering the difference even small changes in digital behavior can have on participants' success, he thinks it's time.