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Trimmed means: comparison of independent samples (Yuen-Welch test)


The Yuen-Welch test is used to compare the trimmed means of two independent samples.

Required input

Yuen-Welch test - dialog box

Select the variables for sample 1 and sample 2. Differences will be calculated as Sample2−Sample1.

Caveat: if the two variables are the same, then the two filters must define distinct groups so that the same case is not included in the two samples.


  • % Trimming: select the percentage of observations that will be trimmed away. For example, when you select 20% then the lowest 20% and highest 20% of observations will be dropped for the calculation of the trimmed mean.
  • Confidence interval: select the required confidence interval for the difference between the trimmed means. A 95% confidence interval is the usual selection.


The results windows displays the sample size, arithmecic mean and its 95% confidence interval, followed by the trimmed mean, the trimmed mean sample size and the 95% confidence interval of the trimmed mean for the 2 samples.

Yuen-Welch test

The report shows the difference between the trimmed means with its 95% confidence interval.

Next follow the test statistic t, the Degrees of Freedom (DF) and the two-tailed probability P. When the P-value is less than the conventional 0.05, the null hypothesis is rejected and the conclusion is that the two trimmed means do indeed differ significantly.

Yuen-Welch test - results

See Calculation of Trimmed Mean, SE and confidence interval for computational details.


  • Wilcox RR (2022) Introduction to robust estimation and hypothesis testing. 5th ed. Elsevier Academic Press.

See also