Research Roadmap

Study design

Study design is not a choice but is a function of matching the study design to the research question that will provide the most unbiased answers. A study design appropriate for the research question is critical to your ability to address the specific aims of your study. The study design is determined by the study objectives and availability of resources; There is a helpful taxonomy for clinical study designs "Algorithm for classification of types of clinical research" (Grimes DA, Schulz KF. Lancet 2002;359, 57-61); note that it is not completely exhaustive but covers most basic clinical study designs.

If you have any questions about choosing the suitable research design, you can ask for a consultation appointment with the Department of Epidemiology and Data Science (EDS) on their Service Portal EDS-Consult.

Sample size

The planned number of study participants is a key aspect of study design, budgeting, and feasibility.

For scientific and ethical reasons, the number of participants needed to provide a reliable answer to the research question(s) needs to be considered carefully. 

The sample size is usually determined using a formal sample size calculation with a balance between clinical and statistical considerations. The clinical and statistical assumptions supporting any sample size calculation should be justified and reported. 

The planned sample size should be large enough to have a high probability (power) of detecting a true effect/difference of a given clinically meaningful magnitude, should it exist. Sample size calculations are generally based on one primary outcome; however, it may also be worthwhile to plan for adequate study power or report the power that will be available (given the proposed sample size) for other important outcomes or analyses. If the planned sample size is not derived statistically, then this should be explicitly stated along with a rationale for the intended sample size (e.g, exploratory nature of pilot studies; pragmatic considerations for trials in rare diseases).  

In instances where information regarding essential elements of a sample size calculation is unavailable, such as a clinically meaningful effect/difference, a pilot study can facilitate the estimation of the anticipated study effect. 

Note that these basic principles for a formal sample size calculations predominantly apply for therapeutic or other types of interventional research projects, e.g. randomized clinical trials. For other type of research questions, such as prognostic research, a sample size calculation is less straightforward. For situations where these basic principles do not apply, consult a biostatistician for assistance.  

For assistance you can ask for a consultation appointment with the Department of Epidemiology and Data Science (EDS) on their Service Portal EDS-Consult.        

Note that the Medical Research Ethics Committee (MREC) and most study grant applications (e.g. ZonMw) ask for a sample size calculation in the approval process.

To get an idea of the feasibility of your research project; make a detailed estimate of the number of subjects that you think you will be able to find for your study:

• How common is this clinical picture?
• How many patients are seen each year for each hospital with such symptoms?
• How many would meet your inclusion and exclusion criteria?
• How many suitable subjects would consent to an invitation to participate in your study?
• Are there competing studies underway?
• How many subjects would you expect to drop out during the study?

In need of more insight into thenumber of patients that meet your inclusion and exclusion criteria? You can request this information from the Research Data Platform (RDP) of the Department of Business Intelligence.