Метод Плакетта – Бермана

Метод Плакетта–Бермана — метод планирования эксперимента, представлен в 1946 году Робином Л. Плакеттом и Дж. П. Берманом.

Метод позволяет выбрать несколько (обычно 3-5) наиболее важных факторов (предикторов). Далее эксперимент может быть оптимизирован с помощью метода поверхности отклика (RSM), метода Бокса-Бенкена (BBD) или центрально составного метода (CCD). Плакет и Берман стремились организовать эксперименты для исследования зависимости некоторой измеряемой величины от ряда независимых переменных (факторов), каждая из которых принимает L уровней, таким образом, чтобы минимизировать дисперсию оценок этих зависимостей с использованием ограниченного числа экспериментов. Взаимодействия между факторами считались незначительными. Решение этой проблемы состоит в том, чтобы найти план эксперимента, в котором каждая комбинация уровней для любой пары факторов встречается одинаковое количество раз во всех экспериментальных запусках (см. таблицу). Полный факторный эксперимент удовлетворял бы этому критерию, но идея состояла в том, чтобы найти меньшие планы. Когда выделить независимый фактор невозможно возникает Спутывающая переменная. Минимальное количество экспериментов, равно 4.

Пример. Цель испытания — определить факторы, которые улучшат срок службы изделия. Исследуются семь факторов. Двухуровневый полный факторный план потребовал бы 27 = 128 прогонов и, таким образом, был бы слишком трудоемким и дорогостоящим. Поэтому вместо этого можно провести восьмикратный эксперимент Плакетта-Бермана.

Для уровней L=2, используется Построение Палея, с квадратными матрицами, все элементы которых равны 1 или −1 (матрицы Адамара). Метод Палея можно использовать для создания матриц размера N, где N кратно 4. В частности, это работало для всех N до 100, кроме N=92. Однако, если N является степенью двойки, результирующий план идентичен дробно-факторному плану, поэтому планы Плакетта-Бермана в основном используются, когда N кратно 4, но не степени 2 (т.е. N=12, 20, 24, 28, 36…). Если кто-то пытается оценить менее N параметров (включая общее среднее), то он просто использует подмножество столбцов матрицы.

Матрицы метода Плакетта – Бермана для серии экспериментов

P.B.4 + + + + – – – + – – – + P.B.8 + + + + + + + + + – – – – + + – + + – – – + – – – + + – – + + – + – – – + – + – + – – – + – – + + – – – + + – + P.B.12 + + + + + + + + + + + + + + + – – – + – – – + + – – – + – – + – + + – + – + + + – – – – + – – + – – + – + + – + – – – + – – + – + + – + + – – – + – – + + – + – + + + – – – + – – + – – + – + + + – – – – + + + – – – + – + – – + – – + – + + + – – – – + – + + + – – + P.B.16 + + + + + + + + + + + + + + + + + + – – – – – – – – + + + + + + – + – – – – + + + – – – + + + – – + + + + – – – – – – + + – + + + – – + + – – + – – – + – + – – + + – – + + + – – – + – – + – + + – + – – – + + – + – – – + – – + – + + – + + – – + + + – + – + – + – – + – – – + + – + – + – + – + – + – – – + – + + – + – – + – + – + – – + – – – + – + + – + + – + – – – + + – – + + – – + – – + + – – + – + + – – + + – – – + + – – – + + + – – – – + + + – + – – – – – – + + + + – + + – + P.B.20 + + + + + + + + + + + + + + + + + + + + + + – + – + – – – – + + – – + – – + + + – + – + 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+ + – + – – + – + – + + – – + + – + – – – + – – + – – + – + – + + – – + + – + – – – + – + – – + + – – + – + – + + – – + – – – + – + – – + + – – + – + – + + – + – – + – + – + + – – + + – – – + + – + – – – + – + – – + + – – + – + – + + – + – – + – + – + + – – – + + – – + – + – + + – + – – + – + – + + – – + + – + – – – + – + – – – + – + – + + – + – – + – + – + + – – + + – + – – – + – + – – + + – – – + – + – + + – – + + – + – – – + – + – – + + – – + – + – + + – + – – – – + + + + – – – – – – + + – – + + + + + – + + + + – – + + – – – + – – – + + – – + + + + + – + + + + – – + + – – – – – – + + + + – – – + – – – + – + – – + + – – + – + – + + – + – – + – + – + + – – + + – + – – – – – – + + + + – – – – – – + + – – + + + + + – + + + + – – + + – + – – – – – + + – – + + + + + – + + + + – – + + – – – – – – + + + + – + P.B.40 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + – + + + + + + + – – + + – – + + – – – – – – – – + + + + – – – – + + – – – – + – + + + + + – – + + – – 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+ + + + + + + + + + + + + + + + + + + + + + + – – – + – + + + – – – – – + – – – + + – + – + + – – + – – + – + – – + + – + + + + – – – + – + + + – – – – – + – – – + + – + – + + – – + – – + – + – – + + + – + + + + + – – – – – + – – – + + – + – + + – – + – – + – + – – + + + – + + + + + – – – – + + + – – + – – + – + – – + + + – + + + + + – – – + – + + + – – – – – + – – – + + – – + + + – – – + – + + + – – – – – + – – – + + – + – + + – – + – – + – + – – + + + – + + + + – + + + + + – – – + – + + + – – – – – + – – – + + – + – + + – – + – – + – + – – + + + – + + – – + – – + – + – – + + + – + + + + + – – – + – + + + – – – – – + – – – + – + + – – + + + – + + + + + – – – + – + + + – – – – – + – – – + + – + – + + – – + – – – + + – – – + – + + + – – – – – + – – – + + – + – + + – – + – – + – + – – + + + – + + + + + – – – – – + – – – + + – + – + + – – + – – + – + – – + + + – + + + + + – – – + – + + – + + + + + – – – + – + + + – – – – – + – – – + + – + – + + – – + – – + – + – – + + + – + + + – + + + + 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+ – – – – – + + + + – + + + + – – + – + – + + + – – – + – + + – – – + – + – + + – – – – + – – – – – + + + + – + + + + – – + – + – + + + – – + – – + + – + – + – + + + – – + – – + + – + + – – – + – + – + + – – – – + – – – – – + + + + – + + + – + – + – – + + – + + – – – + – + – + + – – – – + – – – – – + + + + – + + + + – – + – + – + + – + – – + – + – + + + – – + – – + + – + + – – – + – + – + + – – – – + – – – – – + + + + – + + + + – – + – + – + + – – – – + – – – – – + + + + – + + + + – – + – + – + + + – – + – – + + – + – + – – + – – + + – + + – – – + – + – + + – – – – + – – – – – + + + + – + + + + – – + – + – + + + – – – + – + – + + – – – – + – – – – – + + + + – + + + + – – + – + – + + + – – + – – + + – + + – – – + – – – – – + + + + – + + + + – – + – + – + + + – – + – – + + – + + – – – + – + – + – + – – – – + + + + – + + + + – – + – + – + + + – – + – – + + – + + – – – + – + – + + – – – – – + – – – – + – – – – – + + + + – + + + + – – + – + – + + + – – + – – + + – + + – – – + – + – + – + + 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– – + + – + + – – – + – + + – + – – – – – + + + + – + + + + – – + – + – + + + – – + – – + + – + + – – – + – + – + + – – – – – + + + + – + + + + – – + – + – + + + – – + – – + + – + + – – – + – + – + + – – – – + – – – – – + + + – – + – – + + – + + – – – + – + – + + – – – – + – – – – – + + + + – + + + + – – + + – – + + – – – – + – – – – – + + + + – + + + + – – + – + – + + + – – + – – + + – + + – – – + + – – + – + + + – – + – – + + – + + – – – + – + – + + – – – – + – – – – – + + + + – + + + + – + – – + – + + – – – – + – – – – – + + + + – + + + + – – + – + – + + + – – + – – + + – + + – – + – – + – + – + + – – – – + – – – – – + + + + – + + + + – – + – + – + + + – – + – – + + – + + – – – + – – – – – + + + + – + + + + – – + – + – + + + – – + – – + + – + + – – – + – + – + + – – – – – + + + + – + + + + – – + – + – + + + – – + – – + + – + + – – – + – + – + + – – – – + – – – – – + + – + + – – – + – + – + + – – – – + – – – – – + + + + – + + + + – – + – + – + + + – + – – – + – – – – – + + + + – + + 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