Intended for healthcare professionals

CCBYNC Open access
Research Methods & Reporting

Self controlled case series methods: an alternative to standard epidemiological study designs

BMJ 2016; 354 doi: https://doi.org/10.1136/bmj.i4515 (Published 12 September 2016) Cite this as: BMJ 2016;354:i4515
  1. Irene Petersen, reader in statistics and epidemiology1 2,
  2. Ian Douglas, senior lecturer in pharmacoepidemiology3,
  3. Heather Whitaker, senior lecturer in statistics4
  1. 1Department of Primary Care and Population Health, University College London, London NW3 2PF, UK
  2. 2Department of Clinical Epidemiology, Aarhus University, Aarhus N, Denmark
  3. 3London School of Hygiene and Tropical Medicine, London, UK
  4. 4Department of Mathematics and Statistics, Open University, Milton Keynes, UK
  1. Correspondence to: I Petersen i.petersen{at}ucl.ac.uk
  • Accepted 24 July 2016

The self controlled case series (SCCS) method is an epidemiological study design for which individuals act as their own control—ie, comparisons are made within individuals. Hence, only individuals who have experienced an event are included and all time invariant confounding is eliminated. The temporal association between a transient exposure and an event is estimated. SCCS was originally developed for evaluation of vaccine safety, but has since been applied in a range of settings where exact information on the size of the population at risk is lacking or identification of an appropriate comparison group is difficult—eg, for studies of adverse effects of drug treatments. We provide an overview of the SCCS method, with examples of its use, discuss limitations, assumptions, and potential biases that can arise where assumptions are not met, and provide solutions and examples of good practice.

Summary points

  • The self controlled case series (SCCS) method provides an alternative to established epidemiological designs

  • SCCS is best suited to acute recurrent or non-recurrent events and transient exposures for which precise timings are available

  • Estimation is within individuals and no separate controls are required, hence the method is self controlled, and time invariant factors are cancelled out

  • Follow-up is not censored at the event, so when events can impact on subsequent exposure, care must be taken to ensure analyses are carried out that eliminate or minimise bias

In 1951, Richard Doll and Austin Bradford Hill wrote to all registered doctors in the United Kingdom to obtain information about their smoking habits. This research was groundbreaking as they were one of the first teams to demonstrate a link between smoking and various diseases.1 Since then, epidemiological study designs, such as cohort and case-control studies, have been widely applied in medical research (see supplementary web table w1). There are several situations, however, where standard …

View Full Text