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#HAPTER
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Chapter 5.2
________________________________________________________________________ 109 Drivers (within companies)
who exceed A(8):Yes or No
Employers and drivers from 9 different companies
Baseline measurements:
318 drivers exposed to WBV during their normal working activities. Action limit exceeded by 126 drivers
Drivers (within companies) who exceed A(8):Yes or No 5 companies (1xL, 3xM, 1xS),
182 drivers
Randomization and Stratification:
on company level
4 companies, (1xL, 2xM, 1xS) 136 drivers
Yes: N=61
Intervention programme group (n=65) Content: (high exposure)
1. Health surveillance on individual basis with the aim exposure reduction 2. Informative presentation 3. Brochure
4. Feedback of baseline and follow up field measurements of the VIBRISKS
Yes: N=65 No: N=117
Care as usual group (n=61) Content: (high exposure)
1. Brochure
2. Feedback of baseline and follow up field measurements of the VIBRISKS study
Care as usual group (n=192) Content: (low exposure)
1. Brochure
2. Feedback of baseline and follow up field measurements of the VIBRISKS study
Follow up measurements at 7 months - VIBRISKS questionnaire follow up 2 - Post measurement intervention programme - Field measurement
No: N=75
exposed intervention group, (b) the high exposed ‘care as usual’ group and (c) the low exposed
‘care as usual’ group. Neither the participants nor the researchers were blinded to the treatment allocation at all times.
Figure 1: Flow chart of the study design, the content of the two programmes and the number of drivers corresponding (L=Large, M=medium, S=small)
The intervention programme
We developed an intervention programme to change the behaviour towards WBV exposure in accordance with the, in the field of health education often used, ASE model.9 This ASE model can be used to explain (intended) behaviour by the determinants: attitude (A), social
#HAPTER
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#HAPTER
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#HAPTER
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#HAPTER
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#HAPTER
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Chapter 5.2
________________________________________________________________________ 114 We analyzed the relationship between process variables and outcome with one-way analysis of variance. For this purpose, we calculated tertiles from the process variables that subsequently were used in the analysis of variance. Within the intermediate objectives, mean scores of tertiles will or will not show relevant differences. The F-values and p-values from the one degree of freedom test of the orthogonal polynomials are reported as a measure of trend over the tertiles.8
Results
The study population consists of three hundred and eighteen drivers, working in nine different companies (see figure 1). The study population at T1 decreased to three hundred and fourteen drivers, due to changing of jobs or retirement. The response on the pre-intervention questionnaire (T0) was 75% (n=240). The response on the VIBRISKS questionnaire and the post-intervention questionnaire (T1) was 65% (n=206). The baseline characteristics of the three different groups of drivers are shown in table 1. Based on these characteristics, the formed groups appeared to be comparable for age, height and weight. The response of the employers of the companies was 100% (n=9) at T0 and 89% (n=8) at T1.
Table 1: Number of drivers, drop outs, age, length, weight, driving experience and WBV exposure expressed in the daily dose value A(8) for the three defined groups at baseline (T0).
Outcome: WBV exposure
At T0, eighty six drivers (36%) of the total population of drivers that responded appeared to exceed the action value (0.5 m/s2). At T1, the median WBV exposure shows a minimal, but not significant decrease compared to T0 for group 1 (see table 2). At T1, the median WBV exposure shows no difference compared to T0 for group 2 and the median WBV exposure shows an increase compared to T0 for group 3.
Group 1
Mean (SD) Group 2
Mean (SD) Group 3
Mean (SD) p-value (ANOVA)
Chapter 5.2
________________________________________________________________________ 115 When looking at the proportion of drivers that is exceeding the action value we found a reduction in WBV exposure from exceeding the action value to a WBV exposure level that is beneath the action value for twenty three percent of the drivers (11 out of 47 drivers) in group 1. We also found a reduction in the WBV exposure for twelve percent (5 out of 39 drivers) under the action value of the drivers in group 2. Thirty three drivers who were not exceeding the action limit at T0, were exceeding this action limit at T1, although this exceeding of the action limit was marginal for most of the drivers.
Additional mixed model analysis revealed no significant effect of the intervention programme on the median WBV exposure between the different companies (company level).
Also no significant changes in WBV exposure for the drivers due to implementation of the intervention programme in group 1 compared to group 2 are found (individual level).
Table 2: Median WBV exposure pre test, post test and gain scores and inter quartile ranges at T0 and T1 for the three defined groups.
Process Variables
Knowledge, attitude, intended behaviour and behaviour of the drivers
At T1, respectively 73%, 69% and 73% of the drivers in group 1, 2 and 3 answered correctly on knowledge questions related to WBV issues. All drivers tend to have a moderately positive attitude about WBV related issues and a very moderately positive behaviour towards WBV exposure (see table 3). In all three groups we found an increase in knowledge, with the biggest increase in group 2 (gain 3.0 ± 7.4). No consistent change is found for attitude over the three groups comparing pre and post scores. Group 1 is the only group that showed an increase of 1.5 (± 11.9) in behaviour compared to group 2 and group 3 who are showing a decrease. No big differences are found in the intended behaviour between the three groups; all three groups scored low on this issue, with group 1 in particular.
Mixed model analysis revealed no effect on any of the process variables between the different companies (company level). Also no significant changes in any of the process variables for the drivers due to implementation of the intervention programme in group 1 compared to group 2 are found (individual level).
A(8) m/s2 Group 1 (n=47)
Median
[inter quartile range]
Group 2 (n=39) Median
[inter quartile range]
Group 3 (n=105) Median
[inter quartile range]
Pre test (m/s2) 0.66
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