How clinical trials are designed
Clinical studies for approval of prescription drugs by the United States Food and Drug Administration (FDA) are designed carefully to evaluate how well a drug works (referred to as efficacy or effectiveness) and to evaluate the safety of the drug.
These studies are designed to evaluate measures of effectiveness (referred to as “endpoints”) that are identified before the study is conducted and are based on specific measures that are known to be meaningful and reliable to measure the intended drug effects.
This, among other things, allows for statistical analyses of the study results to substantially reduce the possibility that the results happened by chance and helps to make the results interpretable. In a way, by identifying the analyses ahead of time, it reduces the possibility of subconscious “wishful thinking” where the analyses can be changed inappropriately until the more desirable result is seen.
How comparison groups are created
Studies typically also include a comparison group, that may be a placebo (eg, a sugar pill or a replica of a test medicine that does not contain medicine), or the comparison group may be another treatment known to be used for the same disease or purpose.
Patients in the study are also assigned to the study treatment through something called “randomization,” meaning that they use a system that randomly assigns the treatment to patients to ensure that each study group contains a relatively similar group in terms of their medical background, age, ethnicity, gender, etc. Studies often also include something called “blinding” where the patient or healthcare professional (or both) do not know which treatment the patient is getting (the test treatment or the comparator).
Understanding biases
These features of a study reduce the possibility that the study results are affected by biases or that one study group is more affected by the human perceptions of the patient or the researchers. Biases can also occur as a result of study groups having an imbalance of different types of patients in one group versus another. For example, having more elderly patients in one study group than the other may affect the levels of efficacy shown in one group versus another. This can lead to difficulty in understanding the true treatment effect of the drug.
The reasons for these requirements are so that patients and healthcare professionals can make reliable decisions that are guided by studies with high reliability.
Understanding endpoints
Sometimes, however, researchers that have conducted the studies may evaluate other drug effects that are less rigorous to explore as much as they can about the drug. These effects may be defined ahead of time, but, because the study is not optimized by design or by statistical power, the results evaluating these effects are not as reliable as the primary and main endpoints of the study.
Understanding post hoc analyses
Sometimes, researchers create different analyses after the primary or main results are known, because they may be seeking to learn more about what happened in the study. Because these analyses are conducted after-the-fact, they are referred to as “post hoc” analyses, named after the Latin term meaning “after the event.”
Less rigorous secondary analyses and post hoc analyses are typically considered to be exploratory, because they are exploring more about the drug, but they are not considered to be conclusive. They may be “nice to know” and can be informative, but they can also be difficult to interpret and should always be viewed with caution. They can also be simply misleading if they are inaccurate or untrue with respect to the actual effects of the drug.
When you, as a patient, are evaluating study results, you should understand the primary and main results of the study. If you are viewing other exploratory results, you should understand how they were designed and consider them with caution in light of their limitations. If you are having trouble understanding any type of medical information, including study results, talk to your healthcare provider.
