Fig 1.
Flowchart of the analytical steps for the validation of the VAS demand, control, and support scales against the JDCS questionnaire, following COSMIN guidelines.
Table 1.
Acceptability – Descriptive analysis of main outcome.
Fig 2.
Acceptability – Score of the Karasek model items, as a quantitative variable, using the Visual Analog Scale (VAS) and the JDCS questionnaire.
In the box plot (VAS in blue and Karasek in yellow), the lower and upper sides of the box are the lower and upper quartiles (Q1 and Q3). The box covers the interquartile interval (IQR), where 50% of the data is found. The horizontal line usually splits the box in two and is the median.
Fig 3.
Internal consistency and content validity – Correlation between i) the Visual Analog Scale (VAS); ii) between the VAS and the JDCS questionnaire of Karasek items; iii) Principal component analysis.
Factors that are located close together in the graph are well correlated. The PCA visually shows the proximity of VAS and JDCS for each sub-dimension.
Table 2.
Internal validity – Cut-off determination for visual analog scales (VAS) and concordance with dimensions from the Job-Demand-Control Support (JDCS) questionnaire of Karasek.
Fig 4.
Internal validity – Threshold determination for occupational stress using the visual analog scale (VAS) of job demand, job control and social support (new tool), in reference to the JDCS questionnaire of Karasek (gold standard) – Receptive operator characteristics (ROC) curve; and concordance between the VAS and the JDCS quadrants.
Table 3.
Internal validity – Concordance between quadrants retrieved from visual analog scales (VAS) and quadrants retrieved from the Job Content Questionnaire (JCQ) of Karasek.
Fig 5.
Test-retest reproducibility – Main dimensions agreement between test and retest measures for the visual analog scale (VAS) (new tool), and for the JDCS score (gold standard) – Bland et Altman plots.
The horizontal axis represents the average score between test and retest for each dimension (VAS or JDCS). The vertical axis represents the difference between test and retest scores. The solid orange line shows the observed mean difference (average agreement), and the dashed lines indicate the 95% limits of agreement. The line at y = 0 represents perfect agreement between the two measurements.
Fig 6.
External validity – Relations between VAS and JDCS main items as categorical variables with secondary outcomes variables and agreements between measurement tools illustrated using a polar plot.
The prevalence of high demand, low control and low support was compared between groups using a Chi² test. To quantify the strength of the association between secondary outcomes and each dimension, Cramer’s V was calculated. Agreement was considered low for ≥0.2 points difference, moderate for 0.1 to 0.2 points difference, and high for ≤0.1 points difference.
Table 4.
External validity – Relation between VAS and JDCS (treated as Jobstrain and Isostrain) with secondary outcomes variables and agreements between measurement tools.
Fig 7.
External validity – Relation between VAS and JDCS (treated as Jobstrain and Isostrain) with secondary outcome variables, and agreement between measurement tools illustrated using a forest plot.
The effect of each variable on the risk of Jobstrain/ Isostrain is represented by a dot on a horizontal line. The dots represent the risk of Jobstrain or Isostrain (odds ratio) for each variable, and the line around the dots represent their 95% confidence interval (95 CI). The vertical line represents the null estimate (with a value of 1). Odds ratio with horizontal lines that do not cross the vertical line are significant. Significant variables with an odds ratio <1 are protective factors and those with an odds ratio >1 are risk factors. REF: Reference, i.e., the reference for group comparisons.