Did two different items interact?
To calculate similarity among the items (s(i_j,i_k)) where (i_j) and (i_k) represent two different items, we use cosine similarity measure as shown in Eq. (1).
For example, assume the two applications know the values r a and r b respectively for two different items for the same user.
(r_{i,j}cdot r_{i,k}) and (r^2_{i,j}) represent pairwise multiplications of two different items' ratings (i_j) and (i_k), square of each individual ratings on each item by user (u_i).
When computing feature- based dependencies, two different items have to be identified as sharing some feature.
An unweighted scoring system would calculate a move from one response option to another on two different items as contributing similarly to the overall HRQL score.
Third, because some items contained two concepts such as ' feeling scared or worried', we asked respondents whether these concepts should remain together in one item or whether they should be separated into two different items.
Parental involvement in education was measured with two different items: "how often they speak with teachers" (once a week, once every 2 3 weeks, once a term, less than once a term, never) and "how involved they feel in the adolescent's education" (very involved, fairly involved, not very involved, never involved).
This construct was assessed using two different items: "frequency of parent child arguments" (most days, more than once a week, less than once a week, hardly ever, never) and "quality of parent child relationship" (very well, fairly well, fairly bad, bad).
Questions were designed to (i) assess ease of completion; (ii) evaluate understandability using cognitive probing; (iii) assess whether items with two concepts (such as ' feeling scared or worried') should remain as one item or be separated into two different items; and (iv) assess content validity, or importance of each item to children with cancer in terms of how much it bothered them.
