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.