An uncontrolled study is where all treatments are given to a single group of subjects and therefore, there are no other control or treatment groups available to make comparisons with. Contrary to controlled studies, uncontrolled studies are unable to account for confounding variables because there are no other groups to make comparisons with.
Uncontrolled studies have many limitations which need to be considered. For one, uncontrolled studies are at high risk of being affected by the placebo effect. Sometimes the action of taking a pill may make someone feel or psychologically believe that they are getting better. For example, uncontrolled studies for the common cold may report that most subjects began feeling better after taking treatment, even though their frequency of coughing may not have changed.
The Hawthorne effect is another limiting factor present in these studies1. This effect refers to when patients change their behaviour half-way or part-way through a study. Since there is no control group to draw comparisons with, researchers may interpret these changes as being a result of the treatment when they are related to external factors. For example, going back to the common cold example, maybe part-way through the study a patient began drinking more fluids and thus, began feeling better.
There are other limitations, such as regressing towards a mean value, which are also possible with uncontrolled studies. Essentially, what this all goes to show is that when implementing these types of studies, a researcher needs to be very cautious to not draw invalid or misguided conclusions.
Despite this, uncontrolled studies can be quite useful. For clinical trials which are looking at diseases with a predictable course of action, no control group is necessarily required to make comparisons with and so, these types of studies are more powerful. Additionally, in many clinical trials for medical research, the use of uncontrolled studies is common in the preliminary stages1.
1. Orlando Regional Medical Center. (2013). Study Design. Retrieved from: http://www.surgicalcriticalcare.net/Statistics/design.pdf
Image Credit: Farragut Community School District. (2014). Science Fair Ideas. Retrieved from: http://www.farragutschools.org/vnews/display.v/ART/472e5e671ea1d