Saskia le Cessie is a medical statistician working at the departments of Clinical Epidemiology and Biomedical Data Sciences of Leiden University Medical Center. Saskia is co-lead of Work Package 3. Her research in medical statistics and epidemiological methods is generally inspired by collaboration with medical researchers. The focus of her current research is on epidemiological and statistical methods for observational studies. This involves (1) collaboration in research projects of clinical epidemiologists and other clinical researchers in order to provide cutting edged statistical analyses in observational clinical studies and (2) to perform research on statistical methodology for epidemiological studies. This has resulted in many publications (>350) as co-author on (bio) medical papers and in papers in methodological journals on causal inference, prediction models, mediation analysis, instrumental variables and meta analysis. She is a member of the Dutch Health Council, an associate editor of Clinical Trials and a member of the Steering Group of the STRATOS initiative, which aims to provide guidance in the design and analysis of observational studies.