This study describes the development of the new PROMIS Pediatric Anger Scale based on IRT analyses regarding scale dimensionality, item local dependence and differential item functioning. After determining scale dimensionality, items with LD were next identified and removed resulting in the final PROMIS Pediatric Anger Scale, allowing a variety of possible scoring options that can be tailored to meet the objectives of most clinical research studies.
Two items that exhibited DIF between boys and girls (“I was so angry I felt like throwing something” which had higher scores for boys and “I felt upset” which had higher scores for girls) were included in the final short form. Used together, the DIF for these two items counterbalances almost exactly (see ). The expected summed scores for boys and girls for any level of underlying latent anger are nearly identical. It would not be recommended to construct an even shorter form that includes only one of these two items, but not the other, as such a shorter form may exhibit bias between boys and girls. However, when both items are used they increase precision of measurement over what it would be if they were both omitted.
In addition to investigating gender DIF, we subsequently considered DIF between younger (ages 8–12) and older (ages 13–17) children, and identified a single item, “I felt fed up”, which exhibited DIF after Benjamini-Hochberg correction. This DIF was mainly due to differences in IRT discrimination parameter between age groups. Use of a common discrimination parameter will lead to overestimation of test precision in the 8–12 year age group. The problem is minor, but can be solved by excluding the item. The six-item scale is available from the NIH PROMIS Assessment Center at www.nihpromis.org
, and this site allows the researcher to exclude items from the scale. Several generic self-report HRQOL instruments exist for use in pediatric populations and most attempt to measure at least some aspect of emotional distress. However, these instruments typically do not have an anger specific domain [10
]. Those that do exist are either typically not child self-reports and/or utilized classical test theory rather than taking advantage of IRT analysis in the scale development process [41
]. PROMIS psychometric analyses focus on determining the scale dimensionality and detecting sources of LD and considered final item selection using IRT analyses. Like PROMIS, two of these newer instruments, KIDSCREEN and PedsQL, utilized qualitative research methods for incorporating the child’s perspective during the development process [30
One major challenge prior to applying IRT models to the measurement of emotional distress is resolving issues of dimensionality. Conventional wisdom is that emotional distress scales are less likely to fit unidimensional models [32
]. Often items are sampled from multiple domains (e.g. mood, behavior, somatic symptoms) in order to capture a comprehensive set of latent construct indications. Hence, it is common to observe higher correlations within domains than is expected under the conditional independence assumption of unidimensional IRT models [33
]. One of the initial steps for this project was to develop multidimensional conceptual frameworks that were informed by previous empirical (e.g., factor analytic) and theoretical work as well as to determine the level of resolution at which unidimensional scales could be derived from the domains [3
]. Three constructs of emotional distress were conceptualized: depressive symptoms, anxiety and anger. These results of unidimensionality are consistent with a recent meta-analysis [34
] and other published studies [35
The study population was utilized for testing of all of the PROMIS Pediatric items. Hence, we did not sample specifically the entire range of the anger latent trait and this may be a limitation. Instead we enrolled a large diverse sample of children from community and clinical settings [11
] and we anticipate that we have good coverage across most of the important traits. Future studies should evaluate these items specifically in children recruited from behavioral or anger management programs. The PROMIS pediatric item scale for anger focuses on angry moods and aggression. Other scales focus on these components but may also contain other subdomains such as social skills with peers and authority figures [41
The PROMIS scales provide separate scores for depressive symptoms, anger and anxiety, the PedsQL Emotional Functioning Scale also includes items that indicate depression, anxiety, and anger while the KIDSCREEN Moods and Emotions scale largely measures depressive symptoms, with one item that may indicate anxiety. It also remains a question for future validity studies to determine the usefulness of separate scores for depressive symptoms, anger and anxiety: Though these constructs are highly correlated, they may be differentially predictive or responsive to a particular treatment. In addition, there may be gender differences that might occur. The separate scores of the PROMIS pediatric emotional distress measures permit study of those questions.
Utilizing IRT analysis to identify final items ultimately offers more flexibility for future users of these items. This approach allows researchers the opportunity to select the most useful items for their study design. We proposed a 6-item anger scale; however, a smaller subset of items can also be used and scored on the same metric as the larger set.
The PROMIS pediatric PROs were developed to provide accurate and efficient assessment of important domains of HRQOL for children, including anger. This sample provides initial calibrations of the PROMIS pediatric anger items and the creation of the corresponding PROMIS Pediatric Anger Scale, version 1.0.