Table 2

Degrees of freedom associated with common statistical tests.

Test

Degrees of Freedom


T-test

Independent

n1 + n2 - 2

Paired

n - 1

One-way ANOVA

G - 1 and n - G

Two-way Anova

Main effect of A

GA -1

Main effect of B

GB -1

A × B interaction

(GA -1)(GB -1)

Error

n - GAGB

One-way RM-Anova

Between subjects

G - 1

Error

(n -1)(G -1)

Two-way MixedANOVA

Between subjects

n(G - 1)

Groups

G-1

Error

G(n-1)

Within subjects

N - nG

Obs

Obs - 1

Group × Obs Interaction

(G - 1)(Obs - 1)

Error

N - nG - G (Obs - 1)

Linear Regression

1 and n - 2

Chi-square

(R - 1)(C -1)


n1 = sample size of group one; n2 = sample size of group two; n = total sample size; N = total number of observations (equal to n × Obs); G = number of groups; GA = number of groups for Factor A; GB = number of groups for Factor B; Obs = number of repeated observations on the same subject; R = number of rows; C = number or columns. † "Mixed" refers to the presence of both between and within subjects effects, and should not be confused with mixed effects models described in the text.

Lazic BMC Neuroscience 2010 11:5   doi:10.1186/1471-2202-11-5

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