1. Choose an IV 2. Choose a DV 3.Locate a convenient sample that is due to be exposed to a naturally occurring stimulus (IV) (experimental group) 4.Locate a convenient sample that is NOT due to be exposed to that naturally occurring stimulus (IV) (control group) 5. Collect data on the DV from both populations (pre test). 6. Wait for the naturally occurring IV stimulus to affect the experimental group. 7. Collect data on your DV from both populations (post test). 8. Compare and analyse the two sets of results. Natural Experiment (No control over experimental stimulus)

 Used to refer to situation that is not experimental but is ‘as if’ it was  Not a precise definition – saying your data is a ‘natural experiment’ makes it sound better  Refers to case where variation in X is ‘good variation’ (directly or indirectly via instrument)  A Famous Example: London, 1854

 Regular cholera epidemics in 19 th century London  Widely believed to be caused by ‘bad air’  John Snow thought ‘bad water’ was cause  Experimental design would be to randomly give some people good water and some bad water  Ethical Problems with this

 People closest to Broad Street Pump most likely to die  But breathe same air so does not resolve air vs. water hypothesis  Nearby workhouse had own well and few deaths

 Variation in water supply ‘as if’ it had been randomly assigned – other factors (‘air’) held constant  Can then estimate treatment effect using difference in means  Or run regression of death on water source distance to pump, other factors  Strongly suggests water the cause  Woman died in Hampstead, niece in Islington

Christianson and Hubinette (1993) Their experiment on anxiety The influence of tv on aggressive behaviour (Charlton et al., 2000) (Williams, 1986)

In pairs, Read the examples of natural experiments in your books on page 84 and answer 3.11