2007, Piran, Slovenia
2007, Piran, Slovenia 2007, Piran, Slovenia
Environmental Ergonomics XII Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007 118 Temperature ( o C), RH (%) 90 80 70 60 50 40 30 20 10 0 A 0 10 20 30 40 50 60 70 80 90 100 110 120 130 Time B RH Temp Figure 1. Profile 1 of the air that was circulated through the air cooled garment. Profile 2 was exactly the same but A and B reversed. Water vapour pressure (WVP) during the temperature changes remained constant at 1.744kPa. Statistical analyses A general linear model was used to calculate the root mean square error (RMSE) from three time points during the tests (45, 85,125mins). It was assumed that at these time points the thermal states of the individuals would be the same across the three trials. The RMSE was pooled from each subject for each time point to provide an overall RMSE for each of the scales, the coefficient of variance (CV) was then calculated. Pearson’s product correlations were used to compare the VAS and LS, and the relationship between these scales and T core, T skintorso, T body. Independent t-tests were performed to asses any differences between the two scales and their associations with T skintorso & T body. RESULTS One of the subjects was considered to be highly variable over the three trials compared to the other 8 subjects (i.e. there was no consistency in his voting) and therefore the results that assessed the sensitivity and reproducibility of the scales are displayed in Table 1 with the inclusion and exclusion of the highly variable subject. Reproducibility The results suggest that the VAS scales were more reproducible that that of the LS (Table 1).The amount of pooled within subject variance (RMSE) comprised between 12-25% of the LS, whilst the variance of the VAS scale comprised between 9.7- 19.4% of the scale, depending on the thermal perception examined. In the extreme cases, this variance reduced the number of descriptors the scales could distinguish. The worst case being from 4 to 3 descriptors for the assessment of TTC in the LS and 7 to 5 descriptors for TC in the VAS. Validity Thermal perception displayed on VAS correlated with the LS (r=0.8 to 0.89; P < 0.01). Both scales correlated with T body, T skintorso (r=0.29 to 0.52; P< 0.01).
Cognitive and Psycophysiological Function Table 1. The variability and reproducibility coefficients of the VAS and the LS* Scale VAS LS RMSE CV RMSE CV RMSE CV RMSE CV (N=9) (%) (N=8) (%) (N=9) (%) (N=8) (%) (N=9) (N=8) (N=9) (N=8) TTC 16 18.9 12 14.6 0.5 17.1 0.5 16.5 TC 18 19.8 15 15.7 0.5 15.6 0.4 14.9 TTS 12 11.4 10 10.1 0.8 16.6 0.8 15.0 TS 10 8.3 8 6.7 0.5 9.1 0.4 7.7 *The results are displayed in reference to their scales i.e. for the VAS scales the RMSE is the # of integers on the 160 integer scale. CV= the coefficient of variance. Stable (0-55mins) vs. Dynamic phases (60-130mins). For both the scales, the relationships of TS and TC with both T body andT skintorso were similar for each of the phases examined (stable and dynamic). The exception being the relationship between TS and T body, where both scales had stronger relationships in the stable compared to dynamic phase (VAS: r = 0.64 vs. 0.24; LS: r =0.54 vs.0.23, P < 0.01, respectively). Independent t-tests indicated that the VAS had stronger relationships with T body ,T skintorso and TC than the LS. This occurred for T skintorso /TC in both the stable and dynamic phases (r= 0.50 vs. 0.28 and 0.36 vs. 0.22: P < 0.05, respectively) and TC/T body in the stable phase (r= 0.64 vs. 0.28; P=0.01). DISCUSSION Our findings suggest that the VAS were more reproducible than the LS. Two possible reasons for this are that any change in the LS accounts for 14-25% of the total scale compared to 0.08% in the VAS. Secondly, VAS are displayed as a 100mm line labelled at its ends with the “minimum and the maximum descriptor” for a particular variable, the one used in the present study contains 6-9 descriptors that provide more reference points. The relationship between the VAS, LS and physiological variables indicate that the VAS are at least as valid, and for thermal comfort slightly better, for assessing human thermal perceptions in stable and dynamic, asymmetric thermal environments than the LS. Further work is underway to determine the sensitivity of the VAS to human thermal perceptual changes in dynamic, asymmetric thermal environments. ACKNOWLEDGEMENTS The authors wish to express their gratitude to all subjects who participated in the study. They also wish to thank Julia Allen and Phil Newton for their technical expertise. REFERENCES ASHRAE (1997) ASHRAE Handbook - Fundamentals. Atlanta, ASHRAE Inc. 1997. Fanger, PO. (1970) Thermal Comfort: Analysis and Applications in Environmental Engineering. McGraw-Hill, New York. Zhang, H. (2003) Human thermal sensation and comfort in transient and non-uniform thermal environments. [PhD Thesis]. University of California, Berkley, CA, 94720-1839, USA. 119
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Environmental Ergonomics XII<br />
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana <strong>2007</strong><br />
118<br />
Temperature ( o C), RH (%)<br />
90<br />
80<br />
70<br />
60<br />
50<br />
40<br />
30<br />
20<br />
10<br />
0<br />
A<br />
0 10 20 30 40 50 60 70 80 90 100 110 120 130<br />
Time<br />
B<br />
RH<br />
Temp<br />
Figure 1. Profile 1 of the air that was circulated through the air cooled garment.<br />
Profile 2 was exactly the same but A and B reversed. Water vapour pressure (WVP)<br />
during the temperature changes remained constant at 1.744kPa.<br />
Statistical analyses<br />
A general linear model was used to calculate the root mean square error (RMSE) from<br />
three time points during the tests (45, 85,125mins). It was assumed that at these time<br />
points the thermal states of the individuals would be the same across the three trials.<br />
The RMSE was pooled from each subject for each time point to provide an overall<br />
RMSE for each of the scales, the coefficient of variance (CV) was then calculated.<br />
Pearson’s product correlations were used to compare the VAS and LS, and the<br />
relationship between these scales and T core, T skintorso, T body. Independent t-tests were<br />
performed to asses any differences between the two scales and their associations with<br />
T skintorso & T body.<br />
RESULTS<br />
One of the subjects was considered to be highly variable over the three trials<br />
compared to the other 8 subjects (i.e. there was no consistency in his voting) and<br />
therefore the results that assessed the sensitivity and reproducibility of the scales are<br />
displayed in Table 1 with the inclusion and exclusion of the highly variable subject.<br />
Reproducibility<br />
The results suggest that the VAS scales were more reproducible that that of the LS<br />
(Table 1).The amount of pooled within subject variance (RMSE) comprised between<br />
12-25% of the LS, whilst the variance of the VAS scale comprised between 9.7-<br />
19.4% of the scale, depending on the thermal perception examined. In the extreme<br />
cases, this variance reduced the number of descriptors the scales could distinguish.<br />
The worst case being from 4 to 3 descriptors for the assessment of TTC in the LS and<br />
7 to 5 descriptors for TC in the VAS.<br />
Validity<br />
Thermal perception displayed on VAS correlated with the LS (r=0.8 to 0.89; P <<br />
0.01). Both scales correlated with T body, T skintorso (r=0.29 to 0.52; P< 0.01).
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