Before-After Design


Before-after design is a type of evaluation technique in which the effect of an intervention is assessed by comparing outcomes from a population before and after the intervention. This technique is used to measure the effectiveness of public health interventions, such as the introduction of new public health policies, prevention strategies, or treatments.


Before-after design has been used as an evaluation method since the early 1900s. In 1911, British epidemiologist Major Greenwood used this design to evaluate the effects of an intervention on the mortality rate of London’s water supply. Since then, before-after design has become a widely used evaluation technique for public health interventions.

In the 1950s, epidemiologist Austin Bradford Hill used before-after design to evaluate the effect of the Salk polio vaccine on the incidence of polio. In the 1970s, before-after design was used to evaluate the effects of the Clean Air Act in the United States.

Although before-after design has been used for many years, the technique has been criticized for its potential to produce biased results. Critics argue that changes observed in the population before and after the intervention may not be due to the intervention itself, but rather to other factors such as changes in the population’s behavior or environment.


Greenwood, M. (1911). The mortality of London from enteric fever. British Medical Journal, 2(2561), 1193-1202.

Hill, A.B. (1954). The environment and disease: Association or causation? Proceedings of the Royal Society of Medicine, 48(8), 295-300.

U.S. Environmental Protection Agency. (1972). Clean Air Act. Retrieved from

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