Home > For Consumers > The basic principles of evidence-based...

PubMed Health. A service of the National Library of Medicine, National Institutes of Health.

Informed Health Online [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-.

Informed Health Online [Internet].

The basic principles of evidence-based medicine

Last Update: September 8, 2016; Next update: 2019.

Do you know the trick with the spoon and the champagne bottle? A spoon put into an opened champagne bottle is supposed to keep the champagne fresh and bubbly for longer. But is there any truth to this? And what does this have to do with evidence-based medicine?

The editors of a scientific journal tested this theory in a simple experiment many years ago. To do this, they put not just one, but two, half-empty open bottles in a refrigerator overnight: one with a spoon, one without.

Over the course of the next few days, they had volunteers sample both bottles several times, without telling them which one contained the spoon. This way, if the volunteers believed in the spoon's effect, this wouldn't influence their judgment. The first finding was that the champagne stayed drinkable for a surprisingly long time, taking more than four days to go flat. The second finding was that the participants could not tell the difference between champagne from a bottle with a spoon and from one without. Both bottles went flat equally fast.

Such a simple experiment, with such a clear answer: we might get the impression that a spoon keeps the champagne fresh because the champagne would have stayed fresh for a surprisingly long time anyway.

So what does this experiment have to do with health care?

Quite a lot, actually. Because the same strategy that showed that the spoon doesn't help can be used to test almost all medical interventions, by simply swapping the champagne bottle for "Medical Condition X" and the spoon for "Intervention Y." Of course, it's much harder to judge health issues than the fizziness and taste of champagne, but the principle is the same:

  • There are at least two groups that can be compared to each other
  • Participants' personal biases are minimized as much as possible

These kinds of tests or experiments have become normal in health care in the last 60 years. They are called randomized controlled trials (RCTs). The core idea is to, for example, test the benefits of a new medicine by dividing a group of volunteers into at least two groups by chance (“randomized”). One of the groups will use the new drug, and the other will use an older one or a placebo (dummy drug). Then the treatment outcomes and experiences of the participants are compared.

Just how these studies need to be done to deliver reliable results depends on the illness and the treatment. Sometimes, monitoring 50 or 100 people for a few weeks is enough. Other times, big studies involving several tens of thousands of men and women over many years may be necessary. What's more, single studies are often not conclusive enough to answer a research question on their own. That is why it is usually necessary to consider the results of all the relevant studies.

How one randomized study saved preterm babies from going blind

Today, RCTs are considered the standard for comparing treatments. This was not at all the case in the 1940s. Back then, U.S. neonatologists (experts in the care of newborn and preterm babies) had noticed that babies who were born preterm (too soon) seemed to do better if they got a lot of oxygen. Shortly after, incubators were introduced. It was now possible to keep tiny premature babies in a completely controlled environment and regulate the amount of oxygen around them. The babies' chances of survival increased dramatically.

But at the same time, people noticed that thousands of preterm babies worldwide developed a previously unknown eye disease. Nowadays this disease is called ROP (retinopathy of prematurity). The retina is the light-sensitive layer at the back of the eye. ROP can damage the retina so badly that the baby goes blind.

Nurses in England and Australia suggested it could be because of the oxygen, and published some analyses of the treatment outcomes in their hospitals. But there were many other theories too and more and more research results that contradicted each other.

Controversy about what caused babies to go blind

Hospitals around the world started publishing reports that were supposed to show that preterm babies who were exposed to high concentrations of oxygen did not get ROP. The findings of other research groups suggested that high doses of oxygen were to blame, but couldn't provide definite answers either. In fact, none of the studies at the time were able to reliably pinpoint the cause of the condition.

In early 1953, the controversy rose to a fever pitch. By this time the mysterious disease had blinded around 10,000 infants throughout the world. Finally, the U.S. Public Health Service held a conference that resulted in 18 hospitals agreeing to participate in a randomized controlled trial for three months.

The trial results were published in 1954 and put an abrupt end to the speculation: Babies who were given very high levels of oxygen were three times as likely to develop ROP as babies who were just given a little extra oxygen. Once the research gained widespread attention, the use of oxygen in incubators was reduced around the world, putting an end to the ROP epidemic.

Because of this study, many people came to realize the importance of randomizing people in studies if their aim is to show advantages and disadvantages of a treatment.

How can science and experience be combined in practice?

For a long time, health care relied on doctors, experts and patients to learn what works from observation and experience. But cases like ROP have shown that, without controlled experiments, your conclusions can be very wrong when judging the advantages and disadvantages of treatments. Instead, it's important to combine science and experience, both of doctors and patients.

This basic approach is a founding principle of evidence-based medicine. “Evidence-based” means based on scientific evidence and proof. It means health care that doesn't rely only on personal views and experiences, but looks for the best verifiable evidence for the benefit of a treatment or diagnostic test. This evidence can be found in good-quality studies that examine the advantages and disadvantages.

But medical expertise and experience are also important in evidence-based medicine. In practice, a doctor has to decide whether and how available knowledge can be used in an individual patient's case. This is where experience helps. It's also important to protect patients from too much medical treatment. Good health care doesn’t mean doing "everything" for a patient, but doing the "right thing" for a patient. This helps avoid unnecessary or even harmful interventions.

Another basic principle of evidence-based medicine is to discuss the treatment options with the patient and describe the likely course of their condition if they don’t have treatment. Depending on the patient’s personal views, wishes and expectations, he or she can then make a more informed decision.

What happens if there is no clear answer?

The search for clear and verifiable evidence for the effect of a treatment often doesn’t provide the clear answers you may want. One thing that often remains unclear is whether the benefits of a medical intervention outweigh its disadvantages, such as side effects or the effort involved. Although this can be unsettling, it is valuable information when deciding whether or not to have a treatment or diagnostic test.

Especially if there are no clear answers, doctors need to know the various options and their advantages and disadvantages, and openly discuss them with their patient. This enables the patient to decide for themselves what to do. A wide variety of medical and personal factors can influence this decision.


  • Kirkbride H, Fowler J, Fizzy Fallacy? New Scientist 2000; 5:39.
  • Evans I, Thornton H, Chalmers I, Glasziou P. Testing Treatments. London: Pinter & Martin; 2011. German edition: Gerd Antes (eds.). Wo ist der Beweis? Plädoyer für eine evidenzbasierte Medizin. Bern: Verlag Hans Huber; 2013. Download​.
  • Silverman WA. Personal reflections on lessons learned from randomized trials involving newborn infants, 1951 to 1967. James Lind Library. [PubMed: 16281890]
  • Silverman WA. Retrolental fibroplasia: a modern parable. New York: Grune and Stratton; 1980.
  • Silverman WA. A cautionary tale about supplemental oxygen: the albatross of neonatal medicine. Pediatrics 2004; 113: 394-396. [PubMed: 14754955]
  • IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

    Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. We do not offer individual consultations.

    Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

© IQWiG (Institute for Quality and Efficiency in Health Care)

IQWiG (Institute for Quality and Efficiency in Health Care)

PubMed Health Blog...

read all...

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...