Before-and-after studies

Reviewed and revised 25 May 2014


  • a non-experimental observational study design used to assess the effect of an intervention based on comparison of outcomes prior to its use and afterward
  • most useful in demonstrating the immediate impacts of short- term programs
  • less useful for evaluating longer term interventions, due to the risk of confounders obscuring the effect of the intervention


  • History threat — others events that could affect outcomes occur between the intervention and measurement of outocmes
  • Instrumentation/Reporting threat — validity of of the measurement method changes over time
  • Regression-to-the-mean — outcome measures may appear to improve if the first is a one-time extreme value that naturally becomes more nomral over time
  • Testing threat — taking a measurement may have an effect on the outcome
  • Placebo threat — any intervention may have a non-specific effect on outcomes
  • Hawthorne threat — involvement of outsides may affect the outcome
  • Maturation threat — the outcome may be affected by how the intervention group develops over time, independent of the specific effects of the intervention
  • Dropout threat — the overall characteristics of the intervention group change due to patients dropping out

CCC 700 6

Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.