How to Answer a Probability & Significance Question (AQA A Level Psychology) : Revision Note

How do I answer an AQA A Level Psychology probability & significance question?

• Probability and significance questions can appear in Papers 1 , 2 and 3, and they assess your ability to:

  • demonstrate knowledge and understanding of using statistical tables to determine significance (AO1)

  • apply knowledge and understanding of scientific ideas, processes, techniques and procedures (AO2)

• A typical significance question is presented with a scenario or stem (usually a research study) and is designed to test your AO2 skills

  • E.g., is the psychologist’s calculated value significant? With reference to Table 1, explain your answer [3 marks]

Using statistical tables to determine significance

• After determining the correct statistical test, the psychologist will calculate the data they have collected, which will produce an observed or calculated value

  • This is represented as a test statistic, e.g., U = 40, T = 20

  • You will always be given the calculated/observed value in the exam paper for all the statistical tests except the sign test, as you may have to calculate it yourself

• You may be asked to work out whether the psychologist's results are significant

  • To find this out, the calculated value must be compared to a critical value

  • You will be provided with a table of critical values in the exam paper, e.g.

• There are several steps involved in selecting the correct critical value from the table

  • Is the hypothesis directional (one-tailed) or non-directional (two-tailed)?

  • How many participants (N) were in the study? For some statistical tests, this figure is degrees of freedom instead (df)

  • What is the level of significance (the standard is p≤0.05)?

• Once you have all of this data, you need to find the critical value by looking across the correct row and down the correct column

  • It is ok to highlight or circle the critical value you have chosen on the exam paper

• To determine whether the psychologist's results are significant or not, you will need to compare the calculated value you have been given with the critical value you have chosen

  • There will always be a sentence under the critical values table that tells you whether the calculated value should be equal to/more than or equal to/less than the critical value for the results to be significant

How to write a statement of significance

• Once significance is determined, a statement of significance will then be written, which should include:

  • the calculated value and whether it is equal to, more than or less than the critical value

  • whether the result is significant or not at the stated significance level

  • whether the study has a one-tailed or two-tailed hypothesis

  • the number of participants (N) or degrees of freedom (df)

    • E.g., as the calculated value of U (10.5) is less than the critical value (17), the result is significant at a 0.05 significance level for a two-tailed test, where N₁ = 10 and N₂ = 8

  • You should then include what happens to the null hypothesis

    • If the results are significant, the null hypothesis is rejected and the alternative hypothesis is accepted

    • If the results are not significant, the null hypothesis is accepted and the alternative hypothesis is rejected

      • E.g., this means that we can reject the the null hypothesis and accept the alternative hypothesis