Classification of loneliness using the T-ILS: Is it as simple as it seems?

Student well-being is a growing issue in higher education, and assessment of the prevalence of conditions as loneliness is therefore important. In higher education and population surveys the Three-Item Loneliness Scale (T-ILS) is used increasingly. The T-ILS is attractive for large multi-subject surveys, as it consists of only three items (derived from the UCLA Loneliness Scale). Several ways of classifying persons as lonely based on T-ILS scores exist: dichotomous and trichotomous classification schemes and use of sum scores with rising levels indicating more loneliness. The question remains whether T-ILS scores are comparable across the different population groups where they are used or across groups of students in the higher education system. The aim was to investigate whether the T-ILS suffers from differential item functioning (DIF) that might change the loneliness classification among higher education students, using a large sample just admitted to 22 different academy profession degree programs in Denmark (N = 3,757). DIF was tested relative to degree program, age groups and gender. The framework of graphical loglinear Rasch models was applied, as this allows for adjustment of sum scores for uniform DIF, and thus for assessment of whether DIF might change the classification. Two items showed DIF relative to degree program and gender, and adjusting for this DIF changed the classification for some subgroups. The consequences were negligible when using a dichotomous classification and larger when using a trichotomous classification. Therefore, trichotomous classification should be used with caution unless suitable adjustments for DIF are done prior to classification.