A parallel study is a type of

clinical study Clinical trials are prospective biomedical or behavioral research studies on human participants designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as novel vaccines, drugs, dietar ...

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 In medicine, a crossover study or crossover trial is a longitudinal study in which subjects receive a sequence of different treatments (or exposures). While crossover studies can be observational studies, many important crossover studies are con ...

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 effects 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 ''Intra'' may refer to: * ''Intra'' (album), a 2005 album by metal band Ram-Zet * Intra, a city now part of Verbania, Italy * Intra Airways, British airline * Intra (software), anti Internet censorship Android app by Google. * Intra-frame cod ...

, 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 the process of making something random. Randomization is not haphazard; instead, a random process is a sequence of random variables describing a process whose outcomes do not follow a deterministic pattern, but follow an evolution d ...

– this ensures that the results are accurate and have a lower risk of being biased. Control groups utilizing a

placebo A placebo ( ) is a substance or treatment which is designed to have no therapeutic value. Common placebos include inert tablets (like sugar pills), inert injections (like saline), sham surgery, and other procedures. In general, placebos can af ...

, or active control, are often used in this type of study.

References

* http://hedwig.mgh.harvard.edu/sample_size/size.html {{DEFAULTSORT:Parallel Study Clinical trials Research methods