>> Home >> Stata News >> Vol 30 No 1 (2015 quarter 1) >> Denominator degrees of freedom for mixed-effects models
Stata Release 14: Available now

Denominator degrees of freedom for mixed-effects models

Stata fits linear mixed-effects models and, until now, provided only large-sample inference based on normal and χ2 distributions. In small samples, the sampling distributions of test statistics are known to be t and F in simple cases, and those distributions can be good approximations in other cases. Stata 14 provides five methods for small-sample inference, also known as denominator-degrees-of-freedom (DDF) adjustments, including Satterthwaite and Kenward–Roger. In addition to adjusting the confidence intervals and significance tests reported by Stata's mixed estimation command, small-sample statistics are also provided for subsequent estimation of linear combinations and linear hypothesis tests.

Read even more about denominator degrees of freedom for mixed models in our Stata 14 announcement.


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