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Types of Clinical Trials – Based on Intervention.
Based on Intervention (whether a medicine/investigational product) is given to the subject/patient in the clinical trial, the trials are classified as
* Interventional/Experimental Clinical Trials
* Observational Clinical Trials.
Interventional/Experimental Clinical Trials
In experimental studies the investigator makes an intervention, for example gives a drug, then studies the effects of the intervention.
1. Purpose. The purpose of an experimental trial is to evaluate the effectiveness of an intervention or therapy. The different interventions are applied to similar groups of individuals, who should reflect the population concerned. The differences in observed outcomes should therefore be a direct consequence of the relative efficacy of the interventions tested. Hence, the best evidence of cause and effect may be derived from this type of study.
2. Types of experimental studies. Experimental trials may study differences between subjects or within subjects.
(a) Between subjects (independent data)
• In parallel studies, each group of patients receives a different treatment or intervention concurrently.
(b) Within subjects (paired data).
• Within-subject designs have the important advantage that the subject acts as his or her own control and therefore between-subject variability is removed.
• In paired studies, measurements on each patient are taken more than once, usually in different circumstances, e.g. before and after treatment.
• In cross-over studies, each patient receives each treatment in sequence, with a‘washout’ period between the two (or more) treatments. It is important that the order of the treatments is randomized.
• A matched-pairs design is a parallel study in which each subject in one arm is matched with a subject in the other arm for all known prognostic factors. These two groups are thus closely interrelated and therefore the data may be treated as paired.
Observational Clinical Trials.
• The purpose of an observational study is to look for an association between a cause and an effect, between an exposure to a risk factor and the development of a particular disease.
• Observational studies are particularly relevant in epidemiology which is the branch of medicine that deals with the incidence, cause and prevention of disease.
• When looking for a link, for example, between smoking and lung cancer, investigators cannot use the classical tools of experimental research—they cannot randomize patients into a control group or a treatment group in order to confirm or refute a hypothesis, for obvious reasons. They must use other methods. They can observe a situation and analyse and interpret it, but they cannot intervene. Because subjects cannot be controlled or randomized, many observational studies are fraught with problems of bias.