SSQ (Simulator Sickness Questionnaire) is known to have a complex factor structure, with items loading on multiple dimensions.
In the original study (Kennedy et al., 1993), it is stated that "The N, O, and D scores are then calculated from the weighted totals using the conversion formulas given at the bottom of the table."
Those formulas are:
Nausea = [ Sum obtained by adding symptom scores ] x 9.54
Oculomotor = [ Sum obtained by adding symptom scores ] x 7.58
Disorientation = [ Sum obtained by adding symptom scores ] x 13.92
Total Severity = (Nausea + Oculomotor + Disorientation) x 3.74
It is not clear in the article that how those multipliers, 9.54, 7.58, 13.92 and 3.74 were derived.
Question A: How did they derive those multipliers?
I am working on a Turkish translation of SSQ, and my results are promising. However, it looks like I need to remove some items, and make some changes in scoring.
Attached file contains a comparison of factor weights of my results and Kennedy et al's. original work, besides Bark et al.'s (2013) results on some driving simulator experiments. My results are more similar to Kennedy et al. study, compared to Balk et al study.
The data is collected through 84 participants who had 2 different VR game sessions. SSQ-TR factor analysis is done using Principal Components with Varimax rotation and 3 factors emerged based on eigenvalue>1 assumption.
Question B: I seek for suggestions for factoring the SSQ-TR.
I have some ideas on removing some items and re-adjusting item/load structure, indicated on the shared spreadsheet.
References
Kennedy, R. S., Lane, N. E., Berbaum, K. S., & Lilienthal, M. G. (1993). Simulator Sickness Questionnaire: An Enhanced Method for Quantifying Simulator Sickness. The International Journal of Aviation Psychology, 3(3), 203–220. doi:10.1207/s15327108ijap0303_3
Balk, S. A., Bertola, M. A., & Inman, V. W. (2013). Simulator sickness questionnaire: Twenty years later.
Hi Mehmet, I may be able to give some help with question A:
Firstly however, there is a slight error in the 'Total severity' formula which you present. In your example you give Total Severity = (Nausea + Oculomotor + Disorientation) x 3.74. However, as you have correctly shown above, these subscales each have their own multiplier (9.54, 7.58 and 13.92 respectively). Therefore this total severity calculation would incorrectly include the multipliers from the subscales as well as the Ts multiplier. Instead, the calculation for total severity involves the summation of the three subscale scores prior to applying their multipliers and multiplied instead by the Ts multiplier of 3.74. The correct calculations are as follows:
Nausea = [1] x 9.54
Oculomotor = [2] x 7.58
Disorientation = [3] x 13.92
Total Score = ([1] + [2] + [3]) *3.74
As to the meaning behind the multipliers of 9.54, 7.58 and 3.74, these I believe were included to enable comparison between the scales rather than to add any statistical power. The original text explains: “There is no particular interpretive meaning to the values in the conversion formulas; their function is only to produce scales with similar variabilities on which values can be more readily compared”.
Dear Joseph,
Thanks for the correction. I made a serious mistake when trying to write the question here.
Of those multipliers were for creating a scores value that is comparable to ewcother, I would consider your suggestion and follow a similar approach for SSQ-TR
Hi,
I am using the SSQ for my research and have confusion as to how to calculate the scores from the Likert scale. Do I just add the total of all answers (0-3) or is there a different process to calculate the score? If someone can show by example I will be grateful.
PS The definition from the original paper is unclear to me and no one else has been able to clear it.
Agni Paul,
Briefly, you get the sum of items. Then multiply with the given coefficient value indicated in the paper.
Here is a very brief guide.
https://conservancy.umn.edu/bitstream/handle/11299/201892/SSQ%20Scoring.pdf
Hi,
I haven't been able to understand whether I only have to add the answer of the ones that have a '1' on the chart and then multiply by using the coefficient scores.
For example, if I have received the following answers from a participant -
General discomfort 1
Fatigue 2
Headache 1
Eye strain 1
Difficulty focusing 0
Increased salivation 1
Sweating 3
Nausea 2
Difficulty concentrating 2
Fullness of head 3
Blurred vision 1
Dizzy (eyes open) 2
Dizzy (eyes closed) 1
Vertigo 1
Stomach awareness 0
Burping 1
How do I compute the values for N, O and D from this?
Just as you said. Get the sum of the items marked with 1 for each subdimension. To calculate the subdimension score, for example Nausea, mutiply the result with given coefficient. For the total severity score, get the sum of the three sums (no coefficient included, just sums) and multiply with the total severity coefficient.
The scores should be calculated for each participant. Then you get the mean of participant scores.
So, for the chart that I posted above, the following would be the scores?
N (general discomfort + increased salivation + sweating + nausea + difficulty concentrating + stomach awareness + burping) = 1+1+3+2+2+0+1 = 10 x 9.54 = 95.4
O (General discomfort + Fatigue + Headache + Eye strain + Difficulty focusing + Difficulty concentrating + Blurred vision) = 1+2+1+1+0+2+1 = 8 x 7.58 = 60.64
D (Difficulty focusing + Nausea + Fullness of head + Blurred vision + Dizzy (eyes open) + Dizzy (eyes closed) + Vertigo) = 0+2+3+1+2+1+1 = 10 x 13.92 = 139.2
Total severity = (10+8+10) x 3.74 = 104.72
Which doesn't seem correct?
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