,Aantekeningen a.d.h.v de practica
Aantekeningen practica 1 (t-test, anova, levenes test) :
- The null hypothesis of the one-sample t-test looks like this: H0:μ=some number
- The alternative hypothesis should look like this: H1:μ≠some number
- You can obtain the mean and the standard deviation of the sample by running Analyze >
Descriptive Statistics→ Descriptives. Before you run this, however, make sure that you
have selected only the participants of group 1 with Data > Select Cases.
- what is the t-value? If you choose to do this assignment by hand, you need to
compute the value of t and compare it with the critical value. The formula for
the t statistic is:
- One-sample t-test:
- Alternatively, you can perform the one-sample t-test with SPSS. You can find the
corresponding dialog under Analyze > Compare Means > One Sample T Test
-
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, - two-sample t-test:
-
- You can find the dialog for the two-sample t-test under Analyze→ Compare Means→
Independent Samples T Test. Also see section 12.8 of the book Applied Statistics 1 (pg.
342-345).
In the SPSS dialog you have to specify which two groups you want to compare. In our
case, it’s group 1 and group 4. After placing the group variable in the box named “Grouping
Variable”, click the button named “Define Groups” to define the groups.
To create syntax, click on ‘paste’ rather than on ‘OK’.
- If p<α, we reject the null hypothesis
- ANOVA:
- The null hypothesis of the ANOVA with 5 groups is as follows:
𝐻0:𝜇1=𝜇2=𝜇3=𝜇4=𝜇5
- The alternative hypothesis is: H1: The means are not all equal (note that the
alternative hypothesis in an ANOVA is often written out in words).
- Click Analyze > General Linear Model > Univariate. Choose y as the dependent
variable. Choose group as the fixed factor. Now click on the “Options” button and
check the two boxes named “Descriptive statistics” and “Homogeneity tests”.
Finally, click “Paste” to paste the syntax into the syntax editor, and run it from there by
clicking Run > All.
- Levene’s test:
- One of the assumptions of ANOVA is that the population of which each group is drawn has
the same variance (and hence, the same standard deviation). This assumption is
called homogeneity of variance. The variance in each sample will always differ somewhat,
but this difference should not be significant. That’s why we asked SPSS to perform
“Homogeneity tests”.
- The variances of the groups are not equal in the population, because p is smaller than
alpha Remember that for Levene's test it holds that:
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