Table 5. Intraclass and Cronbach's alpha correlation coefficients between first and second administrations of the Work Productivity and Activity Impairment - General Health (WPAI-GH) questionnaire by administration method.

Scale	Interview/self-administered		Interview/interview
	Intraclass	Cronbach's alpha	Intraclass	Cronbach's alpha
Work time missed (%)	0.76*	0.79*	0.83†	0.84†
Impairment at work (%)	0.91†	0.91†	0.88†	0.88†
Overall work productivity loss (%)	0.92†	0.93†	0.88†	0.88†
Activity impairment (%)	0.77*	0.78*	0.85†	0.85†

^* Good correlation (0.6 – 0.8);

^† Excellent correlation (0.8 - 1). There were no findings of either satisfactory correlation (0.4 – 0.6) or weak correlation (0.2 – 0.4).