PROMIS® Parent Proxy Report Scales for children ages 5-7 years: an item response theory analysis of differential item functioning across age groups

The objective of the present study is to describe the extension of the National Institutes of Health Patient-Reported Outcomes Measurement Information System (PROMISA (R)) pediatric parent proxy-report item banks for parents of children ages 5-7 years, and to investigate differential item functioning (DIF) between the data obtained from parents of 5-7-year-old children with the data obtained from parents of 8-17 year-old children in the original construction of the scales. Item response theory (IRT) analyses of DIF were conducted comparing data from the 5-7 age group with data from the established scales for ages 8-17 across 5 generic health domains (physical functioning, pain, fatigue, emotional health, and social health) and asthma. IRT DIF analyses revealed that the majority of the items functioned similarly with responses from parents of younger and older children. A small number of items were removed from the item bank for younger children, and a few items that exhibited statistical DIF were retained in the pools with the caveat that they should not be used in studies that involve comparisons of younger children with older children. The study confirms that most of the items in the PROMIS parent proxy-report item banks can be used with parents of children ages 5-7. It is anticipated that these new scales will have application for younger pediatric populations when pediatric self-report is not feasible.