Importance of understanding study design
So remember – you need to understand about different types of study designs so that:
- A – you can decide which type of study design is best able to answer your question and
- B – so you know the level and strength of evidence from a particular study design.
We will come back to hierarchy of evidence later on.
One of the problems is that not all research questions can be answered through a RCT either because of ethical issues or for practical issues. Let’s not forget that even when evidence is available from RCTs, it might also be that evidence from other study designs is also relevant.
Experimental and observational studies
Clinical research can be broadly classified into experimental studies and observational studies.
So what are the differences between observational studies and experimental studies?
- Observational studies
This is where the exposure of a subject occurs naturally and is ‘observed’ or recorded by the epidemiologist.
- Experimental studies
In an experimental study (intervention study) the exposure is ‘assigned’ to the patient by the investigator.
|Chapter 5: “Overview of study designs” IN dos Santos Silva, I (1999) (editor) Cancer Epidemiology: Principles and Methods, Lyon: International Agency for Research on Cancer [IARC] publications, WHO||Design of epidemiological studies.|
|Centre for Evidence-Based Medicine (CEBM) Study Designs||Brief guide to the different study types and a comparison of the advantages and disadvantages.|