39- Rephrasing of items, population response options and mode of administration,
translation and cultural adaptation of the instrument, evaluation and documenta-
tion of the changes. - Clinical and psychometric experts review.
- Production of the first draft of the version.
Step IV: Field Testing (1)
- Administration of the instrument to a larger sample of the targeted population—
sample size is calculated considering the number of items. - Psychometric analysis and modification of the tool according to responses.
- Testing the effect of mode of administration on differential item functioning
(DIF). - Rephrasing of items, population response options, and cultural adaptation of the
instrument; evaluation and documentation of the changes. - Clinical and psychometric experts review.
- Production of the modified first draft version.
Step V: Field Testing (2)
- Proper administration of the instrument to a calculated sample of the target pop-
ulation—a control group could be added to test discrimination - Final psychometric analysis—traditional and Rash methods could be used.
- Minimal modification in rephrasing of items, population response options, and
cultural adaptation of the instrument; evaluation and documentation of the
changes. - Clinical and psychometric experts review.
- Production of the final version.
Scoring of Items and Domains
For each item, numerical scores should be assigned to each answer category based
on the most appropriate scale of measurement for the item (e.g., nominal, ordinal,
interval, or ratio scales). Reviewing the distribution of item responses is essential to
ensure that response choices represent appropriate intervals. A scoring algorithm
creates a single score from multiple items. Equally weighted scores for each item
are appropriate when the responses to the items are independent. If two items are
dependent, their collected information is less than two independent items and they
are over-weighted when they are treated as two equally weighted items. Over-
weighting also may be a concern when the number of response options or the values
associated with response options vary by item.
2 A Guide to PROMs Methodology and Selection Criteria