What studies have more validity and why: The importance of clinical trials
With the large amount of medical studies and tests being released to the public these days, it has become difficult to determine which sources to trust and which to neglect. At times, a myriad of studies claiming one theory can be contradicted by powerful clinical trials. A classic example of such an event comes from the early '90s, when beta-carotene (an antioxidant found in fruits and vegetables) was prescribed as a protective agent against cancer and heart disease. After a number of studies showed the positive effects of the chemical, three major clinical trials were released that disproved theories of its being helpful, and actually released evidence that showed it could in fact increase the risk of developing cancer. Attention grabbing, frustrating findings such as this alert the public to be more careful with what to believe and what to challenge.
According to medical experts, there are three specific principles that underlie the search for medical truth and the use of clinical trials to obtain it. Only when these principles are taken into consideration can the trustworthiness of a study be determined. The first is the importance of comparing like with like, which means when two groups are being compared to each other, all factors regarding those groups must be exactly the same, except for the actual factor being studied. In other words, if a study is conducted on beta-carotene, the two groups partaking in the study must be exactly the same except for the one group not taking beta-carotene and the other taking it. When the groups are different, which many times is the case, scientists attempt to compensate by adjusting results to factor in for relevant deviations. Unfortunately, there are certain differences these scientists fail to realize and include, and as a result, faulty conclusions can be reached. With randomized clinical trials, on the other hand, since groups are not alike to begin with, the random distribution of individuals will even out the groups so as to eliminate unfair tilting.
The second major principle regards the size of the study. The rule of thumb here is the larger the group being studied, the more reliable the conclusions. Outcomes of studies are not merely based on a single number derived from the results, but on a range of numbers known as the margin of error. Larger sample sizes create smaller margins of error, which means the results are much more reliable than those with a larger margin.
The third and final principle, not well known by most scientists but extremely important, is based on Bayes' theorem. The theorem basically determines the strength of the supporting evidence separate from the study. Large, definitive clinical trials are usually extremely expensive and take a great deal of time to complete, so they are only performed if a large body of evidence indicates the claim being made is plausible enough to be worth it all. When something plausible is being studied with strong supporting evidence, it will be more credible than a trial studying something implausible, even if both studies have similar variables.
These outlining principles spell out how important randomized clinical trials are in assessing the true validity of studies. Without them, as was the case with beta-carotene, accurate consensus are extremely difficult. Though painstaking and expensive, clinical trials are quite possibly the most important types of studies when it comes to determining the truth.
-As reported in a Sept. '08 edition of The New York Times
-By Greg Gargiulo
