Inter-item correlations
Inter-item correlations were used to explore the relationships among the PRO items. Inter-item correlations were determined using correlation coefficients appropriate for the variables in question between each pair of items at Visit 1. Due to the complexity and variety of the data of interest, using a single type of correlation coefficient would not have been appropriate for all calculations. For item 1–3 (dichotomous scale), the appropriate correlation coefficient was simple matching coefficient, while Pearson’s correlation coefficient was used for the inter-item correlations of item 4–6. Items correlating very highly with one another (