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The evidence that you will use in your professional practice is created by researchers using tried and true practices; these practices are known as the scientific method. Within the scientific method, true experimental designs have features that allow you to assume that causes and effects are linked; without these features, the relationship between cause and effect cannot be distinguished from chance events (see Chapter 5). These experimental designs can further be refined into clinical trials, which use specific methods of planning and interpretation to maximize their application to professional practice.