"Our predilection for causal thinking exposes us to serious mistakes in evaluating the randomness of truly random events....
"We are pattern seekers, believers in a coherent world, in which regularities ... appear not by accident but as a result of mechanical causality or of someone’s intention. We do not expect to see regularity produced by a random process, and when we detect what appears to be a rule, we quickly reject the idea that the process is truly random. Random processes produce many sequences that convince people that the process is not random after all. You can see why assuming causality could have had evolutionary advantages. It is part of the general vigilance that we have inherited from ancestors."Deming chamava ao fenómeno "tampering" e a experiência do funil ilustra o seu efeito na inflação da variabilidade de um sistema.
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Quando monitorizamos o desempenho de um sistema somos tentados a procurar explicações causais para variações perfeitamente aleatórias, logo, muito facilmente, podemos entrar numa roda livre, numa actuação esquizofrénica destinada a remover todo o sintoma de variação... contudo, a variação faz parte dos sistemas normais.
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Por isso, recomendo o uso das cartas de controlo.