Blackwell Reference Online

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Experimentation involves the deliberate manipulation of one or more independent variables followed by the systematic observation of the effects of the manipulation on one or more dependent variables. The emphasis on experimentation in the sixteenth and seventeenth centuries as a way of establishing causal relationships marked the emergence of modern science from its roots in natural philosophy ( Hacking 1983 ). According to the nineteenth-century philosopher John Stuart Mill, a causal relationship exists if (a) the cause preceded the effect, (b) the cause was related to the effect, and (c) we can find no other plausible alternative explanation for the effect. Carefully designed and executed experiments continue to be one of science's most powerful methods for discovering causal relationships. An experimental design is a plan for assigning experimental units to treatment levels and the statistical analysis associated with the plan ( Kirk 1995 : 1). The design of an experiment involves a number of interrelated activities: 1 Formulation of statistical hypotheses that are germane to the scientific hypothesis. A statistical hypothesis is a statement about (a) one or more parameters of a population or (b) the functional form of a population. Statistical hypotheses are rarely identical to scientific hypotheses – they are testable formulations of scientific hypotheses. 2 Determination ... log in or subscribe to read full text