Experimental vs Observational Studies Scientific research involvesdifferent methods of data collection in order to support or reject a proposedhypothesis. Two types of studies that involve the collection of primary data, areobservational and experimental studies. Observational studies can be carriedout in natural environments, such as forests, or fields, but they are also largelyused in epidemiological research. These studies are useful to examine thenatural relationships between two factors. In the biological sciences, when conductingobservational studies, the researcher does not construct or modify theenvironment that the subjects are in. This means there are abiotic and bioticinteractions that may influence the data collected, which creates limitedvalidity of the findings. The researchers cannot accurately measure the effectof one variable on another, due to the presence of external factors that maynot be accounted for.
This lack of control over external factors results in aninability to confidently determine causation between two variables, which is adisadvantage of observational studies. Another disadvantage includes selectionbias and unavoidable systematic differences that do not occur due to thetreatment. This is because the researcher assigns a treatment to a unit, andthe assignment is not random. Additionally, the researcher doesn’t alwayshave control over the subject group, and hence cannot guarantee an unbiasedsample of individuals. For example, observational studies that are carried outfor the purpose of comparison, such as comparing a group of cancer patients whochoose to use chemotherapy, with a group that chooses to forego chemotherapy. Inthis case the researcher has to use a sample of convenience, which can lead tobiased results. However, observational studiesprovide useful data about the interactions between multiple variables that are usuallycontrolled for in laboratory settings, during experimental studies.
Sincenatural processes and interactions in nature do not occur perfectly predictably,data collected from observational studies is an honest reflection of abioticand biotic interactions that influence the relationships of two factors beingstudied. Observational studies can also help gather data about phenomena thatcannot be replicated in laboratory settings. Additionally, they are usefulwhere ethical issues may arise, as patients cannot be denied treatment formedical conditions, hence it would be unethical to conduct an experimentalstudy of patients who do, and do not receive a treatment for a medicalcondition. In experimental studies, researchershave full control over the environment the subject is in, and theirinteractions with external factors.
These studies are usually carried out in alaboratory 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 arecarefully controlled, causation can be determined from results that exhibit acorrelation between independent and dependent variables. This is unlikeobservational studies, where only correlation and not causation can beextracted, due to the external factors that may affect the dependent variablewhich the researcher may not be aware of. Treatments are randomly assignedto avoid biased results, improving the validity of experimental studies. Whenconducting studies involving people, a large sample group of diverse people canbe selected, improving the reliability of the study. These additional levels ofcontrol that occur with experimental studies are advantages of this type ofstudy, and are part of why they are considered the gold standard in scientificresearch.
An example of an experimental study is a scientist testing howdifferent light levels affect plant growth. Different intensities of light maybe exposed to several plants from the same species to measure the effect oflight intensity on growth. A control is often used, which is a unit that is notexposed to any treatment, to confirm that the effects being recorded are due tothe experimental treatments, and not because of other variables. The controlcan be used as a baseline, against which the subjects that underwent treatments,can be compared to. Overall, there are merits anddemerits to both experimental and observational studies. The choice between thetwo is a decision for the researcher conducting the study, and often depends onthe circumstances. Both types of studies are highly valued in scientificresearch.