1. Research Methods:
Data analysis and reporting investigations

2. Results section… • Appropriate selection of graphical representations
• Factors affecting choice of statistical test, including levels of measurement
• The use of inferential analysis, including Spearman’s Rho, Mann-Whitney, Wilcoxon, Chi-squared.
• Conventions of reporting on psychological investigations

3. Appropriate selection of graphical representations
Histogram
Interval
Bar chart
Nominal
Scattergram
Correlation

4. Descriptive statistics
Measures of central tendency
Mean
Median
Mode
Measures of dispersion
Range
Standard deviation

5. Results… • Appropriate selection of graphical representations
• Probability and significance, including the interpretation of significance and Type 1/Type 2 errors
• Factors affecting choice of statistical test, including levels of measurement
• The use of inferential analysis, including Spearman’s Rho, Mann-Whitney, Wilcoxon, Chi-squared
• Analysis and interpretation of qualitative data
• Conventions of reporting on psychological investigations

6. Probability and significance
How likely will it be that a particular result will happen
by chance?
If it is extremely unlikely to have happened by chance,
then the results are thought of as significant.

7. Why do we use a statistical test?
P Value
We want to know the likelihood of the results having occurred by chance
States the percentage probability that the findings have happened by chance.
i.e. how significant?
Psychologists tend to go for 95% certainty. i.e. a 5% likelihood that the results happened by chance.
P = 0.05
Written like this…

8. Why do we use a statistical test?
We want to know the likelihood of the results having occurred by chance

9. In general, psychologists use a 5% significance level. One reason for
Remember!
If this probability is less than 5% (p<0.05 or 1 in 20) then we can ...
accept the experimental or alternative hypothesis and reject the null hypothesis.
If the probability is more than 5% (p>0.05 or 1 in 20) then we must...
accept the null hypothesis and reject the experimental or alternative hypothesis
In general, psychologists use a 5% significance level. One reason for
this is that a 5% degree of uncertainty is usually acceptable if it is not
a life and death matter, whereas, for example, research on the side effects
of drugs is likely to select a 1% significance level because we
would want to be very careful about taking chances.

10. Type 1 – if p-value too lenient Result: significant (so reject null)
What are type 1 and type 2 errors?
Main hypothesis
Null hypothesis
Type 1 – if p-value too lenient
Result: significant (so reject null)
If null is wrongly rejected – type 1 error
Type 2 – if p-value too stringent
Result: non-significant so accept null
If null is wrongly accepted – type 2 error

11. Question Would p<0.05 be more or less stringent than p<0.01 ?
What is a type 1 error?
How can we best reduce this?

12. Read ‘questions about statistics’
VSA website

13. Descriptive v Inferential
Descriptive = visual Graphs Central tendency (mean, median, mode) Measure of dispersion (range, standard deviation) Inferential = significance Related t test Chi square Mann Whitney U Wilcoxon T test

14. How do we know whether it has to be greater or less than the critical value?
Observed value > critical value
greater than
gReateR than – look for an R
speaRman’s Rho
Chi-squaRe
If no R then observed must be less than:
Mann Whitney
Wilcoxon

15. Handout ‘Data type??’ MODE MEDIAN
Nominal data is data that has variables that are basically a category (for example - do people prefer chocolate or
cheese?).
This means that it can only be measured by frequency
e.g.
60 people prefer chocolate
40 people prefer cheese
Ordinal data is data that can be measured. It is numerical in form. This means that we can compare people to one
another by order, rank or position. So - cheese is better than chocolate ... do you ....
1 Very strongly agree
2 Stronlgy agree
3 Agree
4 Undecided
5 Disagree
6 Strongly disagree
7 Very strongly disagree
Or - Mark on a scale of how much you like cabbage.
This then gives a result that can be measured in comparison to others.
MEDIAN

16. & if you’re looking for a relationship or a difference, Its easy!
MEAN
Interval and Ratio data - this is another measured variable. If I asked :
What is your height in centimetres? Or
Name as many bars of chocolate as possible in 30seconds.
How many cheese types can you name in 30 seconds
Once you have worked out which data you are using (practice), and what design it is
& if you’re looking for a relationship or a difference, Its easy!
Relationship = correlation
Difference = experiment

17. Chi squared (x²) test Spearman’s Rho test Mann-Whitney U test
Nominal data?
yes
Chi squared (x²) test
Can be used to find either a relationship
(association) or a difference no
Correlation?
yes
Spearman’s Rho test no
Independent groups?
yes
Mann-Whitney U test no
Repeated measures?
yes
Wilcoxon t-test