Experimental vs Observational Studies


Scientific research involves
different methods of data collection in order to support or reject a proposed
hypothesis. Two types of studies that involve the collection of primary data, are
observational and experimental studies. Observational studies can be carried
out in natural environments, such as forests, or fields, but they are also largely
used in epidemiological research. These studies are useful to examine the
natural relationships between two factors.


 In the biological sciences, when conducting
observational studies, the researcher does not construct or modify the
environment that the subjects are in. This means there are abiotic and biotic
interactions that may influence the data collected, which creates limited
validity of the findings. The researchers cannot accurately measure the effect
of one variable on another, due to the presence of external factors that may
not be accounted for. This lack of control over external factors results in an
inability to confidently determine causation between two variables, which is a
disadvantage of observational studies. Another disadvantage includes selection
bias and unavoidable systematic differences that do not occur due to the
treatment. This is because the researcher assigns a treatment to a unit, and
the assignment is not random.


 Additionally, the researcher doesn’t always
have control over the subject group, and hence cannot guarantee an unbiased
sample of individuals. For example, observational studies that are carried out
for the purpose of comparison, such as comparing a group of cancer patients who
choose to use chemotherapy, with a group that chooses to forego chemotherapy. In
this case the researcher has to use a sample of convenience, which can lead to
biased results.

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However, observational studies
provide useful data about the interactions between multiple variables that are usually
controlled for in laboratory settings, during experimental studies. Since
natural processes and interactions in nature do not occur perfectly predictably,
data collected from observational studies is an honest reflection of abiotic
and biotic interactions that influence the relationships of two factors being
studied. Observational studies can also help gather data about phenomena that
cannot be replicated in laboratory settings. Additionally, they are useful
where ethical issues may arise, as patients cannot be denied treatment for
medical conditions, hence it would be unethical to conduct an experimental
study of patients who do, and do not receive a treatment for a medical


In experimental studies, researchers
have full control over the environment the subject is in, and their
interactions with external factors. These studies are usually carried out in a
laboratory setting which is how external variables are highly controlled.
Researchers can determine the effect of an independent variable, or treatment,
on a dependent variable, or experimental unit. Since all variables are
carefully controlled, causation can be determined from results that exhibit a
correlation between independent and dependent variables. This is unlike
observational studies, where only correlation and not causation can be
extracted, due to the external factors that may affect the dependent variable
which the researcher may not be aware of. 


Treatments are randomly assigned
to avoid biased results, improving the validity of experimental studies. When
conducting studies involving people, a large sample group of diverse people can
be selected, improving the reliability of the study. These additional levels of
control that occur with experimental studies are advantages of this type of
study, and are part of why they are considered the gold standard in scientific
research. An example of an experimental study is a scientist testing how
different light levels affect plant growth. Different intensities of light may
be exposed to several plants from the same species to measure the effect of
light intensity on growth. A control is often used, which is a unit that is not
exposed to any treatment, to confirm that the effects being recorded are due to
the experimental treatments, and not because of other variables. The control
can be used as a baseline, against which the subjects that underwent treatments,
can be compared to.


Overall, there are merits and
demerits to both experimental and observational studies. The choice between the
two is a decision for the researcher conducting the study, and often depends on
the circumstances. Both types of studies are highly valued in scientific




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