c. State whether Bianco and Lecce (2016) should use a one or a two tailed test when checking for significance and why (2)
They would use a one tailed test because the text states that Bianco and Lecce (2016) believe they can improve children’s Theory of Mind test scores in just 4 x 50 minute sessions. This suggests that they would have had a directional hypothesis predicting that test scores will be better after the intervention than before.
d. State the appropriate critical value (1)
The correct critical value for a one tailed test at the 0.05 level when N=9 is 8.
This exam question used command term state so you don’t need to say why this is the correct critical value, however I thought a brief explanation would help as finding N is a little different to some of the other tests and is not very well explained in the Edexcel instructions; basically N = the number of Pps where there was a difference between their two scores. So if there was no difference as both scores were exactly the same, then their D score would be zero. This means they no longer are counted when working out N. In this example, every Pp had difference between their scores and so N was 9 as none of the scores were discounted.
e. State whether Bianco and Lecce (2016) would reject the null hypothesis based on this analysis and why (3)
Bianco and Lecce (2016) would not reject the null hypothesis. They would accept the null and reject the experimental hypothesis, as the observed value of 9 is greater than the critical value of 8. This means that the probability that the null is correct or that results are due to chance is greater than 1 in 20.