Is it inappropriate to compare means of more than one group?

Is it inappropriate to compare means of more than one group?

It is inappropriate because the repetition of the multiple tests may repeatedly add multiple chances of error, which may result in a larger α error level than the pre-set α level. When we try to compare means of three groups, A, B, and C, using the ttest, we need to implement 3 pairwise tests, i.e.,

Which is a comparative case of between group variances?

Figure 1shows two comparative cases which have similar ‘between group variances’ (the same distance among three group means) but have different ‘within group variances’.

When do you need to use multiple comparisons?

Multiple comparisons Multiple comparisons make simultaneous inferences about a set of parameters. When making inferences about more than one parameter (such as comparing many means, or the differences between many means), you must use multiple comparison procedures to make inferences about the parameters of interest.

Which is more important between groups or within groups?

When the between group variances are the same, mean differences among groups seem more distinct in the distributions with smaller within group variances (a) compared to those with larger within group variances (b). Therefore the ratio of between group variance to within group variance is of the main interest in the ANOVA. Open in a separate window

What is the definition of the multiple comparisons problem?

Definition. The multiple comparisons problem also applies to confidence intervals. A single confidence interval with a 95% coverage probability level will contain the population parameter in 95% of experiments. However, if one considers 100 confidence intervals simultaneously, each with 95% coverage probability,…

Which is the best method for multiple comparisons?

However, caution is needed because in some situations the Bonferroni correction may be substantially conservative that actual experiment-wise α error level applied may be lower than 0.05. Tukey’s HSD, Schaffe method, and Duncan multiple range test are more frequently preferred methods for the multiple comparison procedures.

Is the t test inappropriate for more than two groups?

Even when more than two groups are compared, some researchers erroneously apply the t test by implementing multiple t tests on multiple pairs of means. It is inappropriate because the repetition of the multiple tests may repeatedly add multiple chances of error, which may result in a larger α error level than the pre-set α level.

What is the test statistic for independent samples t?

Test Statistic. The test statistic for an Independent Samples t Test is denoted t. There are actually two forms of the test statistic for this test, depending on whether or not equal variances are assumed. SPSS produces both forms of the test, so both forms of the test are described here.