1. 1.3 Data Recording, Analysis and Presentation
Normal and skewed distribution curves
Probability
Using statistical tables of critical values
Parametric and non-parametric tests – Mann Whitney, Wilcoxon, Chi- Squared, Binomial Sign-test and Spearmans

2. Starter
Capture sheet

3. Learning Outcomes Explain why it is the appropriate test to use
Explain why we use inferential stats
Choose the correct statistical test to use
Explain why it is the appropriate test to use

4. Why do we use inferential statistics?
If we carry out data collection and receive this
By looking at the graph is not good enough – open to interpretation, subjective
Inferential stats tell us whether any effect we think we’ve found is real or not, in an objective way

5. Activity 1:
PROBABILITY HANDOUT

6. Workpack Complete the three boxes on the back of your capture sheet
Read through and familiarise yourself with how to do the tests.
There are additional worksheets and workpacks to be completed
Distribution curves
Page 1 +2
Exercise 1 on capture sheet
Levels of significance
Page 2+3
Exercise 2 on capture sheet
Non-parametric tests
Read 3-29
Exercise 3 on capture sheet
Cut and stick handout

7. Non-parametric tests Type of data Independent measures
Repeated measures
Correlation
Nominal
Chi Squared Test
Binominal Sign Test
Ordinal
Mann Whitney U Test
Wilcoxon T Signed Ranks Test
Spearman’s Rho Correlation Coefficient
Interval Ratio
These require parametric data (interval/ratio, data has to have curve of normal distribution, similar variance). For A Level psychology we treat interval ratio as ordinal so use the same tests as ordinal.

8. Activity
Write your own scenario and then ask your partner to figure out what stats test should be used.

9. Type 1 (alpha or α) and Type 2 (beta or β) error
Sometimes psychologists make errors when accepting/rejecting their null hypothesis.
When I have done my stats test I will either accept my alternative hypothesis (and so reject my null) or accept my null (and so reject my alternative). However, errors can be made.

10. The image on the left is the equivalent of someone accepting their alternative hypothesis (they say they have a significant effect when they actually don’t).
Type 1 Error
(false positive)
You’re pregnant.
Type 2 Error
(false negative)
You’re not pregnant.
The image on the right is the equivalent of someone accepting their null (they say they didn’t find a significant result when they actually did).

11. Key Terms
You must understand these terms which you will come across when carrying out statistical tests.
Observed Value – The number produced after the various steps and calculations for a statistical test have been carried out.
Critical Value – A value taken from a statistical test table, which must be reached in order for results to be significant.
Type 1 type 2