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Evidence-based nursing is about applying the best available evidence to a specific clinical question. Different clinical questions require evidence from different research designs. No single design has precedence over another, rather the design chosen must fit the particular research question.1 Questions focused on the cause, prognosis (course), diagnosis, prevention, treatment, or economics of health problems are best answered using quantitative designs, whereas questions about the meaning or experience of illness are best answered using qualitative designs. Many different quantitative and qualitative research designs exist, each with a specific purpose and with strengths and limitations. In this editorial, the most rigorous quantitative designs to address questions of prevention or treatment, causation, and prognosis will be outlined. The next editorial will describe the use of qualitative designs to address questions of meaning or experience.
Questions about the effectiveness of prevention and treatment interventions
The randomised controlled trial (RCT) is the strongest design for questions of whether healthcare interventions are beneficial (ie, do more good than harm). An RCT is a true experiment in which people are randomly allocated to receive a new intervention (experimental group) or to receive a conventional intervention or no intervention at all (control group). Because it is the play of chance alone that determines the allocation, the only systematic difference between the groups should be the intervention. Investigators follow participants forward in time (follow up) and then assess whether they have experienced a specific outcome (fig 1⇓). The 2 most important strengths of RCTs are (1) the random allocation of participants to groups, which helps to ensure that the groups are similar in all respects except exposure to the intervention, and (2) the longitudinal nature of the study, whereby exposure to the intervention precedes the development of the outcome. These 2 features ensure that any differences in outcome can be attributed to the intervention. The …