A recent study shows how therapists have been successfully treating people with arachnophobia, (an extreme and debilitating fear of spiders) using virtual reality (VR) headsets in order to “confront” their clients with 3d digital spiders. The researchers compared the participants’ estimates of the size of a real spider (a 7.5 cm tarantula in a transparent box) with estimates given by non-phobic control group. They also asked both groups to rate their level of fear on a scale of 1-10 as they brought the spiders as close as the Pps could tolerate.  All Pps were then fitted with a VR headset and exposed to four similar spiders in a virtual world for five minutes at a time. This was repeated four times, giving a total exposure time of 20 minutes. Two weeks later participants were again confronted with a real spider and asked to estimate its size, to move it closer and again report their fear levels. For one reason or another, some of the Pps who were present for the original testing were not present for the second stage of the study.

	Table 1: Before Exposure therapy using Virtual Reality
	Experimental Group Pps with arachnophobia		Control Group Pps without arachnophobia
	Estimate of tarantula’s size (cm)	Fear Rating (1-10)	Estimate of tarantula’s size (cm)	Fear Rating (1-10)
Mean	13.5 cm	9.36	8.3 cm	5.75
Standard deviation	1.5 cm	1.2	3.75 cm	4.5

 

	Table 2: After Exposure therapy using Virtual Reality
	Experimental Group Pps with arachnophobia		Control Group Pps without arachnophobia
	Estimate of tarantula’s size (cm)	Fear Rating (1-10)	Estimate of tarantula’s size (cm)	Fear Rating (1-10)
Mean	8.5 cm	5.5	8.1 cm	4.75
Standard deviation	2.5 cm	3.5	1.5 cm	4.5

This extract was based on a study by Shiban et al, (2016).

1. Outline two conclusions that can be determined from the figures in table 1 and 2 (2+2)
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)
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)
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):

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