When it comes to America's healthcare costs, spiraling ever upward, one of the main culprits is unnecessary testing.

Some 130 oft-overused screenings and treatments should be curtailed, according to the two-dozen organizations affiliated with the American Board of Internal Medicine Foundation's "Choosing Wisely" campaign.

Indeed, as Scientfic American pointed out in its article about that initiative, the Instiute of Medicine estimates that $750 billion – three-quarters of a trillion dollars! – was spent on unnecessary services and excessive administrative costs in 2009.

"We are, I hope, at a turning point in American health care where we're realizing you want to have the right health care, not just more health care," Baylor College of Medicine pediatrics professor Virginia Moyer told the magazine.

Well, not quite yet. Many thousands of docs are all too happy to order excessive lab work and imaging – and defensive medicine may be a big reason why. As Doug Campos-Outcalt, a Phoenix, Ariz.-based family physician, told Kaiser Health News, "Nobody ever gets sued for ordering unnecessary tests."

Or what if that wasn't the reason? What if reducing these excesses is a bit easier to explain, if a bit more deeply rooted?

Victoria Shaffer, assistant professor of health sciences in the University of Missouri School of Health Professions, has been working on research related to the psychological roots of how physicians make decisions.

With a degree in quantitative psychology, Shaffer says she's long been interested in studying human judgement in decision-making.

Specifically, she's keen on what makes clinical decisions tick – those made by both doctors and patients in the exam room. Her research is "essentially taking a broad range of academic research in psychology and applying it to specific judgements from the physician and patient perspective," she says.

One of Shaffer's recent projects has shed some interesting light on what drives physicians to order tests – and suggests that the reasons may be more subconscious than we may have thought.

In a study first published in Health Psychology, Shaffer, working with Adam Probst, a human factors engineer at Dallas-based Baylor Scott & White Health, and Raymond Chan, MD, a pediatrician at Children's Mercy Hospitals and Clinics in Kansas City, Mo., took a look at how the lab tests from which a doctor could choose are presented in electronic medical systems.

Shaffer and her team studied how docs picked lab tests using three different designs of order set lists. The first was an opt-in version with no tests pre-selected, as is found on most electronic health records. The second was an opt-out version, in which physicians had to de-select lab tests that weren't clinically relevant. The third had just a few tests pre-selected, based on experts' recommendations.