Can I use ANOVA for small sample size?
ANOVA is robust for deviations from normality when the sample sizes are small but equal. Investigators should try to design studies with equal numbers in each comparison group to promote the robustness of statistical tests.
Does repeated measures ANOVA require equal sample sizes?
Because if you only have repeated measures, it is impossible to use different sample sizes. The very nature of the “repeated” in repeated measures means that there must be values for each subject in both groups.
How big should ANOVA sample size be?
Using the criteria above, the sample size needed for the one-way ANOVA, testing for differences on one independent variable with two groups, is 128, the same as the independent samples t-test.
How does sample size effect ANOVA?
If a one-way ANOVA has low power, you might fail to detect a difference between the smallest mean and the largest mean when one truly exists. If you increase the sample size, the power of the test also increases. For each sample size curve, as the maximum difference increases, the power also increases.
What is the difference between ANOVA and Ancova?
ANOVA is used to compare and contrast the means of two or more populations. ANCOVA is used to compare one variable in two or more populations while considering other variables.
Why can unequal sample sizes be a problem for ANOVA?
Unequal sample sizes can lead to: Unequal variances between samples, which affects the assumption of equal variances in tests like ANOVA. Having both unequal sample sizes and variances dramatically affects statistical power and Type I error rates (Rusticus & Lovato, 2014). A general loss of power.
Do sample sizes need to be equal for t-test?
Even though you can perform a t-test when the sample size is unequal between two groups, it is more efficient to have an equal sample size in two groups to increase the power of the t-test. Welch’s t-test is for unequal variance data.
Why are unequal sample sizes a problem for ANOVA?
Is there a minimum sample size for ANOVA?
On the other hand, if you want to perform a standard One Way ANOVA, enter the values as shown: Now the minimum sample size requirement is only 3. This value applies to each sample or group, so for the 3 Sample ANOVA that would mean each sample has n = 3 for a total number of observations = 9.
What is a good sample size for regression analysis?
Some researchers do, however, support a rule of thumb when using the sample size. For example, in regression analysis, many researchers say that there should be at least 10 observations per variable. If we are using three independent variables, then a clear rule would be to have a minimum sample size of 30.
When to use an ANOVA with SPSS repeated measures?
SPSS repeated measures ANOVA tests if the means of 3 or more metric variables are all equal in some population. If this is true and we inspect a sample from our population, the sample means may differ a little bit. Large sample differences, however, are unlikely; these suggest that…
What does sphericity mean in repeated measures ANOVA?
Assumptions Repeated Measures ANOVA. Sphericity. This means that the population variances of all possible difference scores (com_1 – com_2, com_1 – com_3 and so on) are equal. Sphericity is tested with Mauchly’s test which is always included in SPSS’ repeated measures ANOVA output so we’ll get to that later.
Which is the null hypothesis for repeated measures ANOVA?
Generally, the null hypothesis for a repeated measures ANOVA is that the population means of 3+ variables are all equal. If this is true, then the corresponding sample means may differ somewhat. However, very different sample means are unlikely if population means are equal.
Which is the best effect size for ANOVA?
ANOVA – (Partial) Eta Squared Partial eta squared -denoted as η2 – is the effect size of choice for ANOVA (between-subjects, one-way or factorial); repeated measures ANOVA (one-way or factorial);