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Abstract:
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An observational study investigates effect of a treatment when the treatment is not randomized. A central concern is unmeasured differences between the treatment and control group other than the treatment. After adjustments have been made for measured covariates in an observational study, an association between treatment and outcome is ambiguous: an association may be an effect caused by the treatment, or a reflection of unmeasured differences between the treatment and control groups. Quasi-experimental devices enlarge the set of considered associations with the intention of reducing this ambiguity. Classical quasi-experimental devices include pre-treatment outcomes and multiple control groups. Recently new quasi-experimental devices have been developed such as evidence factors, differential effects and computerized construction of quasi-experiments. We will discuss these new quasi-experimental devices in the context of real observational studies.
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