What is the Noncentrality Parameter? (A new part added to the most recent version of SPSS in ANOVA's tables)

The noncentrality parameter (λ) is a value used in noncentral distributions (like the noncentral F-distribution) to compute:

Observed power

Confidence intervals

Critical values for hypothesis tests

It quantifies how far the true distribution is from the null distribution. When λ = 0, the F-distribution is central (i.e., under the null hypothesis).

A larger λ means a larger effect — the further the true mean is from the null.

Noncent. Parameter (λ): A theoretical value that determines the shape of the F-distribution under the alternative hypothesis.

Higher λ>>>Greater deviation from null → stronger evidence for the effect.

Used for>>>Calculating observed power and confidence intervals.