10 Matching Annotations
  1. May 2019
    1. Multiple comparisons: It is not good practice to test for significant differences among pairs of group means unless the ANOVA suggests some such differences exist. Nevertheless, I admit it is tempting to take another look at the comparison of G1 with G3 (ignoring the existence of G2 and perhaps assuming normality), but then you should use a Welch t test to account for the differences in sample variances, and you should not make claims about the result unless the P-value is as low as .01 or .02. Looking at that difference more carefully might prompt a subsequent experiment.

      Test for significance among pairs when the overall f test is not significant.

  2. Apr 2019
    1. There are two tests that you can run that are applicable when the assumption of homogeneity of variances has been violated: (1) Welch or (2) Brown and Forsythe test. Alternatively, you could run a Kruskal-Wallis H Test. For most situations it has been shown that the Welch test is best. Both the Welch and Brown and Forsythe tests are available in SPSS Statistics (see our One-way ANOVA using SPSS Statistics guide).

      ANOVA is robust against violation of the assumption of equal variances, but...

    2. However, platykurtosis can have a profound effect when your group sizes are small. This leaves you with two options: (1) transform your data using various algorithms so that the shape of your distributions become normally distributed or (2) choose the nonparametric Kruskal-Wallis H Test which does not require the assumption of normality.

      ANOVA is robust against violation of normality, but...

    1. Favorable changes occurred in z-scores for weight (one-tailed p < 0.04) for age and gender among children in the combined center- and home-based intervention compared to comparison children at posttest.

      Here is an example of a study that used an one-tailed test as opposed to a two-tailed test.

      Challenge for readers: Dig into the Methods section and find out why the researchers used an one-tailed test.

  3. Mar 2019
    1. From this data, it can be concluded that cholesterol concentration in the diet group was statistically significantly higher than the exercise group (U = 110, p = .014). Depending on the size of your groups, SPSS Statistics will produce both exact and asymptotic statistical significance levels. Understanding which one to use is explained in our enhanced guide.

      Phrasing results for the Mann-Whitney U-test.

    1. We performed some manipulation checks to examine the internal validity of the perceptual-cognitive skill tests and any learning effects as a result of watching the same video clips multiple times