Uniform DIF was present for one item by age and two items by sex.
Only uniform DIF was present for one item by age and one item by sex.
Two items demonstrated minimal differential item functioning by age: Seeing how people react (11), and Limited endurance (18), with logit values 0.61 and 0.59, respectively.
DIF items were found by age (6 items), employment status (6 items), social class (2 items), mood (2 items), hip v knee (2 items), social deprivation (1 item) and body mass index (1 item).
However, a low uptake of this Medicare Benefits Scheme (MBS) funded item by age-eligible patients has been reported [ 13, 14].
The Physical, Cognitive and Summary scales all showed good fit to the model, were unidimensional, and free of differential item functioning by age, sex and time.
However, in the 10-item version, item #1 functioned differently by age group, and items #2 and #4 functioned differently by education level.
The summary score from the OV28 symptom scales for the hormonal items was influenced by age, with older women less likely to report hot flushes (OR=0.25, P-value<0.001).
When these items were analysed by age group, the maximum number of prescriptions billed was by patients between 75 and 84 years, the most polymedicated group (up to 40% of the total prescriptions billed).
The age related DIF The age related DIF Figure 4 is a scatter showing differential item functioning plots for each domain of the SGRQ item by the age comparison.
