Often epidemiological studies are performed by analyzing data sources such as questionnaires, medical records, medical devices, or laboratory tests. Data preparation is the process of cleaning and transforming raw data prior to processing and analysis. It is an important step and often involves reformatting, making corrections and combining data sets to enrich the original data. This directory collects scripts to the most essential steps related to the collection, cleaning, and statistical processing of data for epidemiological studies, which embrace all steps from raw data to the final dataset for statistical/mathematical modelling.