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The 1.5 Sigma Shift

1990
  • Mikel Harry
Engenheiro de controle de qualidade que analisa métricas de capacidade de processo na fabricação.

(Imagem gerada apenas para fins ilustrativos)

The 1.5 sigma shift is an empirical correction used in Seis Sigma calculations to account for the long-term dynamic variation of a process. It posits that over time, a process mean will tend to drift by about 1.5 standard deviations from its short-term centered position. This shift is the reason a 6 sigma process corresponds to 3.4 DPMO, not the theoretical 2 defects per billion.

Disclaimer: the 1.5 sigma shift is one of the most debated aspects of Six Sigma. It originates from the observation that short-term data, collected over a brief period, typically shows less variation than long-term data from the same process. This is because over longer periods, factors like tool wear, material variations, operator differences, and environmental changes cause the process mean to drift. The 1.5 sigma value was determined empirically by Motorola engineers as a reasonable general estimate for this drift. By incorporating this shift, Six Sigma provides a more realistic, long-term view of process performance. The calculation for DPMO is thus based on the probability of an outcome falling outside a specification limit that is [latex]4.5\sigma[/latex] from the drifted mean ([latex]6\sigma – 1.5\sigma[/latex]). Critics argue that the 1.5 value is arbitrary and that a well-controlled process should not drift this much. Proponents argue it’s a pragmatic adjustment that makes the Six Sigma standard more applicable to real-world industrial processes.

UNESCO Nomenclature: 3308
Engenharia e tecnologia industrial

Tipo

Sistema abstrato

Interrupção

Incremental

Uso

Uso generalizado

Precursores

  • Walter A. Shewhart’s work on common and special cause variation
  • long-term vs. short-term process capability studies
  • empirical observations of industrial processes
  • control chart theory

Aplicações

  • calculating long-term process capability (Cpk, Ppk)
  • setting realistic quality targets in manufacturing
  • risk assessment in financial modeling
  • reliability engineering for long-life products

Patentes:

NA

Ideias de Inovação Potencial

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Related to: 1.5 sigma shift, process drift, six sigma, dpmo, statistical process control, process capability, long-term variation, motorola, quality control, standard deviation.

Contexto histórico

The 1.5 Sigma Shift

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(Caso a data seja desconhecida ou irrelevante, por exemplo, "mecânica dos fluidos", é fornecida uma estimativa aproximada de seu surgimento notável)

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