Adequacy of the measurement models was tested before testing the full structural model. To test the full structural model, all constructs ( Figure 1) were entered into the model and all factor loading, specified paths, covariance, measurement errors and disturbances were estimated simultaneously. Since the model contained categorical variables, Weighted Least Square with mean-and variance-adjusted estimation (WLSMV) was used to estimate the standardized parameter (b) for each path [43] . With this kind of estimation, chi-square difference testing is inappropriate. We therefore used the Comparative Fit Index (CFI), Tucker-Lewis Index (TLI) and Root Mean Squared Error of Association (RMSEA) to evaluate the model fit to the data. A CFI.0.95, TLI.0.95 and RMSEA,0.05 indicate a good fit of data to the model [43] . The analysis was conducted in Mplus 6.0 for Windows [43] . The proportion of missing values ranged from 0.1% for ''In the past one week, have you ever worried about catching influenza A/H1N1'' to 10.1% ''did you wash hands after sneezing, coughing or touching nose in the past 3 days''. Missing data were handled with multiple imputation to generate 10 datasets which were summarized into one for subsequent analysis. Multiple imputation was performed in AmeliaView [44] .