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Statistical Significance and p values
Thursday, 31 May 2012
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.
Thursday, 31 May 2012
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.
Thursday, 31 May 2012
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
Thursday, 31 May 2012
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
Thursday, 31 May 2012
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
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
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
