Goodness of Fit Test
A goodness of fit test uses χ² = Σ((O-E)²/E) to compare observed frequencies to those expected under a hypothesized distribution. It tests H₀ that the data follow a specified distribution. Degrees of freedom = (number of categories - 1 - parameters estimated from data).
Real World
A quality analyst at Cadbury tests whether the number of defective chocolates per batch fits a Poisson distribution by comparing observed defect counts to expected frequencies.
Exam Focus
Subtract one degree of freedom for each parameter estimated from the data, not just for the number of classes.
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