Study Designs

There are different types of clinical research. The design used in any study is dependent on the

question being investigated. This section will look at some of the most commonly used study

designs:

Cohort studies

Case control studies

Cross sectional surveys

Case reports

Clinical trials

Cohort Studies

This type of study design follows specific groups of people (e.g. those with a disease,

with exposure to a treatment or who are alike but for one lifestyle factor such as

occupation or high alcohol consumption etc.) over a period of time to see how

outcomes differ when they receive different treatments and interventions.

This study design allows you to collect specific data over a given time, and allows for interaction

with participants. However cohort studies can be expensive and can take years to complete.

Examples of research carried out using this type of design can be seen in the papers:

Observational cohort study of HIV-infected African children by Laufer et al (2006).

Do we adequately respect the potential of routine primary health care services in reducing

neonatal mortality in developing countries? The example of the Denizli cohort by Uner et al

(2010).

Case Control Studies

In these studies cases are matched to measure the impact of an intervention or disease. People

with a specific disease or experiencing a specific intervention (the cases) are compared with

individuals who do not have the disease or have not experienced the intervention (the controls).

Once matched data is collected from both groups, it is then compared to investigate whether other

characteristics (e.g. nutrition) are different.

The aim is to try to uncover what caused the outcome in one group but not the other. To reduce

the number of factors that could be related to the difference in cases and controls, all participants

should be recruited from the same population.

This study design can be subject to recall bias (events can be reported differently between the two

groups e.g. those with the disease may remember interventions or exposures more easily than

those in the control group). However this design is relatively inexpensive, can be completed in a

short period of time and can be carried out by individuals or small groups of researchers.

Examples of research carried out using this type of design can be seen in the following papers:

Results from an international case-control study of childhood brain tumours: the role of

prenatal vitamin supplementation by Preston-Martin et al (1998).

Changing patterns in demography of cleft lip-cleft palate deformities in a developing country:

the Smile Train effect – what lies ahead? by Patil et al (2011).

Cross Sectional Surveys

These surveys are used to gather information from a specified number of cases (e.g. individuals,

systems, etc) in a population at a single point in time. The design is used to examine factors

expected to remain unchanged during the period of data collection. These surveys are a basic

variety of descriptive or observational epidemiology.

Mosby’s Dictionary states that:

“this study design aims to describe the relationship between diseases (or other health-related

states) and other factors of interest as they exist in a specified population at a particular time,

without regard for what may have preceded or precipitated the health status found at the time of

the study.”

This study design is relatively quick and easy but it does not allow for a distinction to be made

between cause and effect.

Examples of research carried out using this type of design can be seen in the papers:

Quality of pharmacies in Pakistan: a cross-sectional survey by Butt et al (2005).

Prevalence of stroke and related burden among older people living in Latin America, India and

China by Ferri et al (2011).

Case Reports

Case reports are the detailed histories of single cases. They provide the

symptoms, signs, diagnosis, treatment, and follow-up of an individual patient.

Vandenbroucke (2010) listed six topics that most case reports focus on and

these are:

unexpected associations between diseases or symptoms

unexpected events in the course of observing or treating a patient

findings that shed new light on the possible pathogenesis of a disease or an adverse effect

unique or rare features of a disease

unique therapeutic approaches

a positional or quantitative variation of the anatomical structures

The advantage of this type of design is that case reports allow us to uncover unexpected effects,

new diseases, etc., which can lead to increased knowledge. However, as case reports are

essentially ‘anecdotal’ they are the lowest level of scientific evidence, because they have not been

gained through rigorous scientific study.

Examples of research carried out using this type of design can be seen in the papers:

Occupational asthma in Korea by Oh & Kim (2010).

Obstructive jaundice at the initial presentation in small-cell lung cancer by Ochi et al (2010).