This document discusses statistical significance and p-values. It explains that statistical significance determines whether differences in experimental and control groups are real or due to chance. Tests of significance are used to measure the influence of chance, and results are considered statistically significant if p < 0.05, meaning there is less than a 5% probability the results are due to chance. The document provides examples of interpreting p-values in experiments.

1. Statistical Significance
and p values
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2. What is statistical
significance?
• In any experiment there is going to be
difference in the results obtained from the
experimental and control groups.
• Statistical significance tells us the difference
is real on not just due to chance.
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3. Tests of Significance
• Tests of statistical significance can be used to
determine the extent to which chance has
operated
• The significance level of any difference is
called p value, with p standing for
probability.
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4. Setting p value
An acceptable p value for results is established before the experiment
is conducted. In general general, psychologists accept a level of p <
(equal to or less than) 0.05 as being statistically significant in order to
conclude that results are due to the influence of the independent
variable and not to chance.
A 0.05 significance level occurs when the probability of chance is 5 or
fewer times in 100 repetitions of the research
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5. Practice Question
Question 22
In an experiment looking at sex differences in working memory, which of the following is most
probably a significant result?
A. p < 0.01
B. p < 0.1
C. p > 0.05
D. p > 0.01
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6. Answer
Question 22
In an experiment looking at sex differences in working memory, which of the following is most
probably a significant result?
A. p < 0.01
B. p < 0.1
C. p > 0.05
D. p > 0.01
Students who chose option C apparently fixated on the figure ‘0.05’, and failed to recognise the
significance of the inequality sign – in this case, ‘greater than’.
Thursday, 31 May 2012

7. Practice
Question 22
A psychologist tests memory recall under two different conditions. A test of significance finds
that p > 0.05. This means that there is a
A. less than 5 in 100 chance that the results are due to chance.
B. greater than 5 in 100 chance that the results are due to chance.
C. less than 5% difference between the results of the two conditions tested.
D. greater than 5% difference between the results of the two conditions tested.
Thursday, 31 May 2012

8. Answer
Question 22
A psychologist tests memory recall under two different conditions.
A test of significance finds that p > 0.05. This means that there is a
A. less than 5 in 100 chance that the results are due to chance.
B. greater than 5 in 100 chance that the results are due to chance.
C. less than 5% difference between the results of the two conditions tested.
D. greater than 5% difference between the results of the two conditions tested.
Thursday, 31 May 2012