Tarantula Mark Scheme and Answer

  1. Outline two conclusions that can be determined from the figures in table 1 and 2 (2+2)
  • Answers needed to draw from evidence in the Tables.
  • Using data was critical due to the use of the command term “determine” in the question
  • One mark was awarded for identifying conclusions and one mark for awarded for elaborating with the use of data
Conclusion 1: Exposure therapy using virtual reality headsets was successful for treating arachnophobia as the Pps with arachnophobia showed a decrease in their fear ratings from an average of 9.36 before therapy to 5.5 after therapy, a reduction of 3.86 on a 10 point scale.

Conclusion 2: Fear of spiders in those with arachnophobia may be linked to an exaggerated perception of the size of the spider as before therapy they estimated that the live spider was 80% bigger than it really was, e.g. 13.5 cm when it was really only 7.5 cm, compared with after therapy when they perceived that the spider was only 13% bigger than it really was, (8.5 cm compared with 7.5 cm)  

2. State one reason why the researcher in this study has used the mean as the measure of central tendency for the estimates of the tarantula’s size. (1)

  • Answers should have referred to the level of measurement that was used for the estimate of tarantula’s size, e.g. centimetres so ratio data
  • Could have referred to fact that mean is the most sensitive and most powerful of the three measures of central tendency because all the scores are used (if you only mentioned all scores used this didn’t gain credit only if you also said “most sensitive because…”
Option 1: The researcher used the mean as the measure of central tendency for the estimates of the tarantula’s size because the estimates were given in centimetres and these are standardised units with a true zero meaning the data is ratio and therefore the mean is the most suitable measure of central tendency.

Option 2: The researcher used the mean as the measure of central tendency for the estimates of the tarantula’s size because this is the most powerful and sensitive measure of central tendency and this is because it uses all the data points from each Pp in the condition.

3. The researcher wishes to know whether the reduction in the estimate of the tarantula’s size before and after VR exposure therapy is statistically significant for the participants with arachnophobia. State which statistical test should be used and why (3)

  • Needs to refer to the correct experimental design, e.g. repeated meaures
  • Needs to refer to the correct level of measurement, e.g. ratio which can be collapsed to ordinal
  • Needs to refer to the hypothesis of the study whjcih is testing for a difference between conditions NOT a correlation or relationship between two variables.
The researcher would have used a Wilcoxon’s. This is because they are testing for a difference between two conditions (before and after the VR exposure therapy). Secondly the experimental design is repeated measure as we are looking at the same groups of participants and comparing their scores before and after rather than looking at two different groups of people and finally the level of measurement for the estimate of the spider’s size is ratio, (centimetres are standardised units with a true zero) and this can be collapsed to ordinal data.


4. Explain two possible problems with this study which may mean that VR exposure therapy is not as effective as it may seem (2+2):

Problem 1: On problem is the results could be seen as lacking internal validity. The participants may have told the researcher that they felt less fearful and estimated the spiders size as smaller in the second condition due to demand characteristics, i.e. they knew that they were expected to feel better and think differently after the therapy/intervention and therefore they answered accordingly by saying they were less fearful on the 10 point scale and saying they thought the spider was smaller. They were basically giving socially desirable answers. Possibly they may also have said this as they did not wish to have to remain in the study and potentially face their fears again in another round of VR therapy.

Problem 2: Some of the Pps were not able to be part of the second part of the study and had they been involved the results may have looked rather different, meaning the results again may lack generalisability as the sample is less representative than it was at the beginning. For example, the people who did not wish to participate and dropped out second time around may be characterised by the fact that they were petrified by the VR experience and in fact this made their phobias worse and they wanted nothing to do with the research again. Had their results been included the average fear rating and estimate of spider size might have been much higher and exposure therapy would have seemed less effective as a consequence.