Cross-sectional studies represent observational research and involve collecting and analyzing data from multiple research subjects at one and the same period of time. This design is an optimal choice for evaluating the prevalence of disorders and risk factors. One example would be surveying a large sample of adult pet owners to explore the prevalence of allergy symptoms in those owning pets with fur and making assumptions about animal species and breeds that might be associated with an increased risk of allergies.
In contrast to that, case-control research involves analyzing a series of cases with an outcome of interest. Cases are compared to a control group, the members of which do not display this outcome. In this research design, the comparative analysis focused on some supposed risk factors for the condition in question sheds light on whether the risk factor status and the fact of developing an outcome are related.
An example of case-control research could be a comparative evaluation of teenagers with clinically confirmed dissociative identity disorder and their peers without this condition and assessing whether exposure to sexual or physical abuse as a child increases the risk of developing the disorder later in life.
Cohort studies also utilize observational methods and can be both prospective and retrospective. A typical prospective study involves recruiting a group of individuals meeting a set of predetermined criteria but having no outcome of interest yet, making sure that the group involves enough representatives that have and do not have the exposure of interest, and observing how many individuals will develop the outcome in the future.
In retrospective studies, participants’ exposure to the risk factor in question is assessed retrospectively. As an example, this design can be helpful in exploring the predictors of gestational diabetes in primigravidas. It is possible to recruit a sample of primigravida women in the first month of pregnancy, some of whom have hypertension, observe them, collect data on the cases of gestational diabetes developed after the study’s start, and evaluate the connection between elevated blood pressure and gestational diabetes.
Finally, randomized studies are experimental and use random assignment to groups. Being a gold standard of research, RCTs involve assigning participants to the experiment or control group and comparing the effects of drugs or treatments against a placebo in placebo-controlled RCTs or against a standard treatment option in active comparator designs.
Crossover trials, another subtype of randomized research, involve exposing both groups to both treatments being compared but in a different order. One possible example of randomized research would be an active comparator RCT in which patients with MDD are randomly assigned to a novel drug, such as Rapastinel, or a standard first-line antidepressant, Zoloft, and their symptoms’ severity is comparatively analyzed later.