Research Study Designs

By Ahmad Jamil Malik

Types of research study designs

Research study designs can be divided into two groups based on the interventions involved i.e., Experimental study design and Observational study design. If we are doing any intervention in our study, like introducing a medicine or running a trial of a new drug, it will be experimental study design but if we are simply observing a population or comparing two groups of a population, it will be observational study design.

Experimental study design:

It can be further divided into two sub-groups based on random allocation of the subjects in our experiment. If we are randomly allocating the subjects into the two groups, in our experiment, it will be called as Randomized Controlled Trial (RCT) but if we are non-randomly or selectively dividing the subjects into the two groups, it will be called as Non-Randomized Controlled Trial (NRCT)

Observational study design:

It can also be further divided into two subgroups based on the presence of a comparison group or the involvement of the testing of any hypothesis in our study. If we are comparing any two groups in our study, it will be called as Analytical observational study. If we are not comparing any two groups, OR we are simply studying the details of any representative population, it will be termed as Descriptive observational study.

Design of a randomized controlled trial:

Experimental studies:

1. Open Label Study: Both the participant and the researcher know the treatment participant is receiving.
2. Single Blind Study: The researcher knows but the participant does not know about the treatment they are receiving.
3. Double Blind Study: Neither the researcher nor the participant knows which treatment they are receiving.

Analytical study design:

Observational studies, where establishing a relationship (association) between a ‘risk factor’ (etiological agent) and an outcome (disease) is the primary goal, are termed analytical.

• Kinds of analytical studies: -

1. Cohort study: It can be either prospective or retrospective. In this study, two groups with unknown outcomes are compared based on a supposed risk factor.
2. Case control study: It is always retrospective. In this study, two groups with known outcomes are compared based on a supposed risk factor
3. Cross-sectional study: In this study, risk factors and outcomes are measured at the same point in time.

Descriptive study design:

When an epidemiological study is not structured formally as an analytical or experimental study, i.e., when it is not aimed specifically to test a hypothesis, it is called a descriptive study.

• Kinds of descriptive studies: -

1. Case Report / Series: A series of cases of a specific condition, or a series of treated cases, with no specifically allocated control group.
2. Descriptive Cross-Sectional: Cross-sectional studies entail the collection of data in a population. It does not aim at testing of hypothesis about any association
3. Ecological: When the unit of observation is an aggregate (e.g. family, clan or school) or an ecological unit (a village, town or country).