%K Causal analysis, Sample size, Power, Meta-analysis, Planning %O This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions. %D 2022 %A TP Morris %A M van Smeden %V 142 %I Elsevier BV %T Causal analyses of existing databases: The importance of understanding what can be achieved with your data before analysis (commentary on Hernán) %L discovery10134915 %J Journal of Clinical Epidemiology %P 261-283