This article explains the difference between the different study design types in the Study Settings tab. The choice of a study design type influences the availability of certain features and the pricing of the study. 

Prospective 

Prospective studies are specific types of research projects with a defined set of research outcomes, where the data is collected prospectively. An example of a prospective study is a randomized controlled trial or a prospective observational study. 

Retrospective 

Retrospective studies indicate that the data is already collected, but needs to be transferred to Castor for further storage, data management, analysis, etc. This would normally involve existing data import and no further collection of data. 

Registry

A registry is a database of patients with a certain condition that can be further used for different types of prospective or retrospective studies. Registry databases are with a broader goal in mind (not always specific research outcomes) and are maintained for longer periods (sometimes decades on end). Biobanks can also be a type of registry, for example. A rare disease cohort, for example, would be a registry. 

Other

All studies that do not fall under the previously mentioned categories can be classified under 'Other'. You can select this type for example, if you are conducting a retrospective study that requires the query module.