Table 5: Research design categories and the specific needs they each address

Status of knowledge regarding problem	Type of research question	Appropriate research study design
Knowing that a problem exists but knowing little about its characteristics or possible causes.	What is the nature/ magnitude of the problem? Who is affected? How do the affected people behave? What do they know, believe, think about the problem and its causes?	Descriptive studies: Cross-sectional surveys
Suspecting that certain factors contribute to the problem (or are associated with it)	Are certain factors indeed associated with the problem? (e.g. lack of pre-school education related to low school performance? Is low-fibre diet related to carcinoma of the large intestine?)	Analytical (Comparative) studies: Cross-sectional comparative studies Case control studies Cohort studies
Having established that certain factors are associated with the problem: Establishing the extent to which a particular factor causes or contributes to the problem	What is the cause of the problem? Will the removal of a particular factor prevent or reduce the problem? (e.g. stopping smoking, providing safe water).	Cohort studies Experimental or quasi-experimental studies
Having sufficient knowledge about cause(s) to develop and assess an intervention that would prevent, control or solve the problem	What is the effect of a particular intervention/strategy? (E.g. treating with a particular drug; being exposed to a certain type of health education) Which of two alternate strategies gives better results? Which strategy is most cost-effective?	Experimental or quasi-experimental studies