A randomized controlled trial of 1,816 Swiss primary care doctors found that personalized letters showing how their vitamin D testing compared to peers’ practices reduced unnecessary vitamin D testing by 3.66 tests per 100 patients. According to Gram Research analysis, this simple, low-cost intervention successfully reduced wasteful medical testing without requiring complex programs or additional resources.
According to Gram Research analysis, a major study of Swiss doctors found that sending personalized letters comparing doctors’ practices to their peers’ practices successfully reduced unnecessary vitamin D testing. Researchers tracked over 1,800 primary care doctors and found that those who received letters showing how their vitamin D testing compared to other doctors’ testing rates reduced their tests by about 3-4 per 100 patients. The study also tested whether similar letters could encourage doctors to prescribe cheaper generic medications instead of brand-name drugs, but this approach didn’t work as well. This research shows that sometimes the simplest solutions, like showing doctors how their practices compare to others, can help reduce wasteful medical spending.
Key Statistics
A 2026 randomized controlled trial of 1,816 Swiss primary care doctors found that peer comparison letters reduced vitamin D testing by 3.66 tests per 100 patients compared to doctors who received no intervention.
In the same study, letters encouraging generic medication prescribing increased generic prescribing by only 0.57 percentage points, a change too small to be statistically significant.
The vitamin D testing intervention showed heterogeneous effects, with reductions ranging from 1 to 7 tests per 100 patients depending on individual doctor characteristics and baseline practices.
The Quick Take
- What they studied: Whether sending doctors personalized letters showing how their vitamin D testing and medication prescribing practices compared to other doctors’ practices would reduce unnecessary tests and encourage cheaper generic drug prescribing.
- Who participated: 1,816 primary care doctors in Switzerland, divided into three groups: one group received letters about vitamin D testing, another received letters about generic medications, and a control group received no special letters. The study ran from November 2020 to December 2021.
- Key finding: Doctors who received letters about vitamin D testing reduced their testing by 3.66 tests per 100 patients compared to doctors who didn’t receive letters. However, letters about generic medications didn’t significantly increase generic drug prescribing.
- What it means for you: This research suggests that simple, low-cost interventions like peer comparison letters can help reduce unnecessary medical tests. If you’re a patient, this might mean fewer unnecessary vitamin D tests. If you’re a healthcare administrator, this shows a promising way to reduce wasteful spending without complex programs.
The Research Details
This was a randomized controlled trial, which is considered the gold standard in medical research. Researchers randomly divided 1,816 Swiss primary care doctors into groups. Some doctors received personalized letters showing how their vitamin D testing rates compared to other doctors in their region and highlighting professional guidelines about when vitamin D testing is actually necessary. Other doctors received similar letters about generic medication prescribing. A control group of doctors received no special intervention.
The study tracked these doctors’ actual practices over time to see if the letters changed their behavior. Researchers measured two main outcomes: the number of vitamin D tests ordered per 100 patients and the percentage of medications prescribed as generics instead of brand names.
This design is powerful because randomly assigning doctors to different groups helps ensure that any differences in outcomes are actually caused by the intervention (the letters) rather than by differences between the doctors themselves.
This research approach matters because it tests a real-world solution in actual medical practice rather than just in a laboratory. The study included hundreds of real doctors treating real patients, making the results more applicable to everyday healthcare. Additionally, the researchers looked at whether the intervention worked differently for different types of doctors, which helps identify which doctors might benefit most from this approach.
This study has several strengths: it was a randomized controlled trial (the highest quality study design), it included a large number of doctors across an entire country, it had a control group for comparison, and it was published in a prestigious medical journal (NEJM Evidence). The results were statistically significant for vitamin D testing (P<0.001), meaning the findings are very unlikely to be due to chance. However, the study was conducted in Switzerland, so results might differ in other countries with different healthcare systems.
What the Results Show
The vitamin D testing intervention was successful. Doctors who received letters showing how their vitamin D testing compared to peers reduced their testing by an average of 3.66 tests per 100 patients. To put this in perspective, if a typical doctor sees 100 patients per year, this means about 3-4 fewer unnecessary vitamin D tests per year. The researchers were very confident in this result (95% confidence interval: -5.42 to -1.89 tests per 100 patients), and the finding was statistically significant.
However, the generic medication intervention did not work as expected. Doctors who received letters encouraging generic prescribing showed only a tiny increase of 0.57 percentage points in generic medication prescribing, and this increase was so small it could easily be due to chance (P=0.37). This suggests that simply comparing doctors’ prescribing practices to peers’ practices isn’t enough to change medication prescribing habits.
Interestingly, the researchers found that the vitamin D testing intervention worked differently depending on which doctors received it. Some doctors reduced their testing by just one test per 100 patients, while others reduced it by as many as seven tests per 100 patients. Doctors who already prescribed many generic medications at baseline were more likely to increase their generic prescribing after receiving the intervention letter.
The study found that doctors with low baseline rates of generic prescribing did not increase their prescribing after receiving the intervention letter. This suggests that the intervention may only work for doctors who are already somewhat inclined to prescribe generics. Additionally, the heterogeneity analysis (which looked at differences between doctor subgroups) revealed that the vitamin D testing intervention’s effectiveness varied significantly depending on the doctor’s baseline practices and characteristics.
Previous research has shown that many healthcare interventions to reduce unnecessary care have had limited success. This study adds to the growing evidence that peer comparison and professional norm feedback can be effective for some types of low-value care (like unnecessary vitamin D testing) but not others (like generic medication prescribing). The results align with behavioral economics research suggesting that people are influenced by how their behavior compares to others’ behavior.
The study was conducted only in Switzerland, so results may not apply to other countries with different healthcare systems, insurance structures, or doctor populations. The study only tracked doctors’ behavior for about one year, so it’s unclear whether the effects would last longer. The intervention worked well for vitamin D testing but not for generic prescribing, suggesting that different types of low-value care may require different intervention strategies. Additionally, the study didn’t measure patient outcomes or whether reducing vitamin D testing actually improved patient health.
The Bottom Line
Healthcare systems should consider using peer comparison letters as a low-cost intervention to reduce unnecessary vitamin D testing. This approach appears to be effective and requires minimal resources compared to other quality improvement programs. However, different interventions may be needed to address other types of low-value care, such as unnecessary medication brand-name prescribing. Confidence level: High for vitamin D testing reduction; Low for generic medication prescribing.
Healthcare administrators and policymakers should care about this research because it offers a cost-effective way to reduce wasteful spending. Doctors should care because it shows how peer feedback can help them align their practices with professional guidelines. Patients should care because reducing unnecessary tests can mean fewer medical procedures, lower costs, and less time spent on unnecessary healthcare. Insurance companies should care because reducing unnecessary tests directly reduces healthcare costs.
Based on this study, doctors who received the intervention letters showed changes in their vitamin D testing behavior relatively quickly, within the study period of about one year. However, the study didn’t track whether these changes persisted beyond one year, so it’s unclear how long the effects last. Healthcare systems implementing this intervention should expect to see changes within 6-12 months.
Frequently Asked Questions
Do peer comparison letters actually reduce unnecessary vitamin D testing?
Yes. A 2026 study of 1,816 Swiss doctors found that personalized letters comparing their vitamin D testing to peers’ rates reduced testing by 3.66 tests per 100 patients, a statistically significant reduction that suggests this low-cost intervention works.
Can the same approach reduce unnecessary medication prescribing?
Not effectively. The same study found that peer comparison letters increased generic medication prescribing by only 0.57 percentage points, which is too small to be meaningful. Different strategies may be needed for medication prescribing.
How much money could healthcare systems save using this approach?
The study didn’t calculate direct cost savings, but reducing 3-4 vitamin D tests per 100 patients annually could save significant money across large healthcare systems. Vitamin D tests typically cost $30-50 each, so savings would accumulate quickly at scale.
Does this intervention work the same for all doctors?
No. The study found that effectiveness varied widely, with some doctors reducing testing by just 1 test per 100 patients while others reduced it by 7 tests per 100 patients, suggesting individual doctor characteristics influence how much they respond to peer feedback.
How long do the effects of peer comparison letters last?
The study tracked doctors for about one year, showing sustained effects during that period. However, the research didn’t measure whether effects persisted beyond one year, so long-term durability remains unclear.
Want to Apply This Research?
- Track the number of vitamin D tests ordered per month and compare your rate to the average for similar doctors in your region. Set a goal to reduce unnecessary testing by 10-15% over the next quarter.
- If you’re a healthcare provider using a practice management app, enable peer comparison notifications that show how your vitamin D testing rates compare to colleagues. Review your vitamin D testing orders monthly and question whether each test aligns with current clinical guidelines before ordering.
- Implement a monthly dashboard showing your vitamin D testing rate per 100 patients compared to regional and national benchmarks. Track which patient populations you’re testing most frequently and whether those tests are clinically justified according to current guidelines.
This research describes findings from a study conducted in Switzerland and may not apply to all healthcare systems or populations. The study shows that peer comparison letters can reduce vitamin D testing but does not prove that reducing vitamin D testing improves patient health outcomes. Before making changes to your healthcare practices or decisions, consult with your healthcare provider or medical team. This article is for informational purposes only and should not be considered medical advice. Individual vitamin D testing decisions should be made based on your specific health situation and your doctor’s clinical judgment.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.
