HL Psychology Internal
Assessment
Inferential Statistics
HL requirements for maximum 3 marks.

An appropriate inferential statistical test has been chosen and explicitly justified.
Results of the inferential test is accurately stated. The null hypothesis has been
accepted or rejected according to the results of the statistical test. A statement of
statistical significance is appropriate and clear.

The information you have obtained from participants takes the form of raw data.
This should go into the appendices, and you should use your results to calculate
descriptive statistics appropriate to your to data.

The test you choose is dependent on the level of of measurement of your data and
whether you used independent samples or repeated measures.

There are three statistical tests that are generally used for the IA. You should refer to
the design of your experiment and the level of measurement of your data in
justification of your choice of the statistical test.

Here are the necessary details for the statistical tests that are recommended
for the IB internal assessment.

The Chi Square test: used for nominal data in an independent samples
design in an experiment testing a difference between two conditions.

The Mann Whitey U test: use for at least ordinal data in an independent
samples design in an experiment testing a difference between two
conditions.

The Wilcoxon Signed Ranks test: used for at least ordinal data in a repeated
measures design in an experiment testing a difference between two
conditions.

If you are truly familiar with the t test then you might consider its relevance.
Once you have carried out the test, you will need to make a statement that explains
what you have done. For example.
A Chi-squared was carried out because the data were nominal and two independent
samples were being compared. A significant difference was found (formula) and we
can therefore reject the null hypothesis.
Significance decisions. “We have come to an absolutely fundamental principle
underpinning much social science research – the notion of rejecting the null hypothesis
at a certain level of significance. In a sense, the level of (p≤0.05) is the golden standard
by which differences or relationships are counted as significant or not.
If a result is significant (p<0.05) the null hypothesis is rejected.
If a result is not significant (p>0.05) the null hypothesis is retained.
A directional hypothesis

Very often, we state before we test the hypothesis in which direction of the
results will fall. Our hypothesis id directional and the appropriate statistical
test of the hypothesis is called one-tailed.

Once you have collected the data. Decide which test you need to
administer. Only one person in your group needs to work out the
mathematics.

If you need help Mr Teather has kindly agreed to help formulating your
critical values and administering the correct test. You must speak to me first
and I will arrange the appropriate time for help.
Using Tests of Significance – The General procedure

Choose appropriate statistical test

Calculate statistical test

Compare the test with the critical values. These can be found in the back of
the Research methods text book, or mathematics statistic books, or online.

Decide which side of the critical value your result is on.

Report the decision.