A parallel study is a type of
clinical study
Clinical trials are prospective biomedical or behavioral research studies on human subject research, human participants designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as novel v ...
where two groups of
treatments, A and B, are given so that one group receives only A while another group receives only B. Other names for this type of study include "between patient" and "non-crossover". This is unlike a
crossover study where at first one group receives treatment A and later followed by treatment B while the other group receives treatment B followed by treatment A. There are, however, certain characteristics that allow for differentiation between these two types of trials. For example, a parallel study would be more appropriate if any concerns about
carryover effect
The carryover effect is a term used in clinical chemistry to describe the transfer of unwanted material from one container or mixture to another. It describes the influence of one sample upon the following one. It may be from a specimen, or a rea ...
s were present. This type of study might also be more beneficial if the disease or disorder being studied has a likely chance of progression during the time in which the study takes place. One significant issue with parallel studies, though, is the concept of
intra subject variability, which is defined as variability in response occurring within the same patient.
The two treatment groups in a parallel study can either consist of two completely separate treatments (i.e. different drugs), or simply different doses of a common drug. One major aspect of a parallel study is
randomization
Randomization is a statistical process in which a random mechanism is employed to select a sample from a population or assign subjects to different groups.Oxford English Dictionary "randomization" The process is crucial in ensuring the random alloc ...
– this ensures that the results are accurate and have a lower risk of being biased. Control groups utilizing a
placebo
A placebo ( ) can be roughly defined as a sham medical treatment. Common placebos include inert tablets (like sugar pills), inert injections (like saline), sham surgery, and other procedures.
Placebos are used in randomized clinical trials ...
, or active control, are often used in this type of study.
References
* http://hedwig.mgh.harvard.edu/sample_size/size.html
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Clinical trials
Research methods