Probability and
Significance
Unit 4 – Research Methods
Learning Objectives

Use knowledge from previous lessons to answer past exam questions on
hypotheses

Explain why psychologists use inferential statistics

Define what is meant by probability & identify different levels of probability
(e.g. p=0.05)

Outline which level of probability and significance psychologists use AND why

Outline what is meant by type 1 and type 2 errors

Identify and justify the use of FOUR inferential statistics used in Psychology
Starter – Past exam questions

Answer the exam questions based on yesterday’s lesson on hypotheses

Swap your answers

Peer mark using mark scheme

Any targets?
Probability and Significance

Lets imagine we notice that history students are more sociable than
psychology students

Write a suitable hypothesis and remember to operationalise…
Probability and Significance

Go through the worksheet completing the tasks
Type 1 error

A type 1 error refers to a situation in which we assume that our findings show
something when they don’t!
= rejecting a null hypothesis that is true
= wrongly accepting the alternative hypothesis
=assuming the results were due to the IV when they were in fact due to chance

Therefore we should have kept the null hypothesis rather than rejecting it!
K. Christopher, La Retraite School
Type 2 error

A type 2 error refers to a situation in which we may miss something that is
actually happening!
= accepting a null hypothesis that is false
= wrongly rejecting the alternative hypothesis
=assuming the results were due to chance when they were in fact due to the IV

Therefore we should have rejected the null hypothesis rather than accepting
it!
K. Christopher La Retraite School
Test your knowledge

If we reject the null hypothesis when it is actually true, we are making a…

The significance level normally set in psychology is…

For a result to be significant, the test statistic must be equal to or ______
than the critical value

How do we define probability?

If we accept the alternate hypothesis when it is actually false, we are making
a…
Inferential Statistics

To decide on the statistical test, we first need to think about the type of data we
have….

Is it:

Nominal

Ordinal

Interval/ratio

Each of you has a particular data type – describe this type and use an example
Nominal data
Ordinal data
Interval/ratio data
Which Test?

Using your booklet and textbook, create a poster/information sheet to help
researchers know which test to use

This should include
-
The four tests
-
Which data type they use – with a brief description of the data
-
Which experimental design is used – with a brief definition of each design
1. Which test would you use?
Participant
number
New Mathematics
Help Scheme
Participant
number
No Scheme
implemented
1
11
11
14
2
12
12
13
3
9
13
12
4
8
14
16
5
11
15
14
6
14
16
15
7
10
17
19
8
7
18
20
9
15
19
16
10
9
IV = Whether or
not given Maths
help Scheme
DV = Maths test
score
2. Which test would you use?
Participant
Study time (mins)
Test score (%)
1
100
60
2
25
47
3
95
70
4
60
53
5
10
41
6
75
51
7
80
61
8
45
44
9
55
45
10
85
61
3. Which test would you use?
Participant
number
Neutral Words
Emotionally
threatening words
1
14
15
2
18
16
3
19
19
4
20
14
5
16
19
6
15
10
7
20
16
8
18
15
9
19
18
10
20
18
IV = Whether word
presented is neutral
or emotionally
threatening
DV = Recall of words
4. Which test would you use?
Art Students
Science
Students
Row Total
Extroverted
19
10
29
Introverted
11
15
26
Column Total
30
25
Total: 55
IV = Whether
Art Students or
Science Students
(Natural Experiment)
DV = ExtroversionIntroversion score
Answers
1.
Mann Whitney
2.
Spearman’s rho
3.
Wilcoxon
4.
Chi square
Your Task

Complete the past exam questions on inferential statistics
Learning Objectives

Use knowledge from previous lessons to answer past exam questions on
hypotheses

Explain why psychologists use inferential statistics

Define what is meant by probability & identify different levels of probability
(e.g. p=0.05)

Outline which level of probability and significance psychologists use AND why

Outline what is meant by type 1 and type 2 errors

Identify and justify the use of FOUR inferential statistics used in Psychology