This thesis concerns the short-term state of and changes in self-rated participation in domestic life, peer relations and, to some extent, school. Participants were adolescents with and without self-reported impairments and long-term health conditions. It is a thesis in disability research and a functional perspective on the participation of adolescents in everyday activities is applied. The thesis is one of several sub-studies in the Swedish research program LoRDIA (Longitudinal Research on Development in Adolescence).

Aim: The aim was to study the relationships between individual and environmental factors and participation in a two-time point longitudinal study within the frame of the health classification system ICF-CY. The aim was also to study the impact of environmental and individual factors on self-reported participation in adolescents with and without impairments and long-term health conditions.

Methods: The study designs in the four studies are cross-sectional (studies I and II), and prospective longitudinal (studies III & IV). A combination of person-based (such as cluster analysis in studies II and IV) and variable-based methods (such as ANOVA, multiple regressions, logistic regressions (studies I, II, III and IV)) were used.

Results: When linking items from a questionnaire aiming to measure mental health in adolescents to codes in the International Classification of Functioning, Disability and Health, Children and Youth version, latent coding is preferable to manifest coding. The focus should be on the underlying meaning of the item and the primary aim of the scale from which the item originated should be taken into consideration. Concerning the self-rated experience of participation, it was stable over time when investigated from a two-time point longitudinal perspective. Results revealed that type of impairment cannot be considered the sole predictor of the experience of participation at home, with peers and in school. Factors in the microsystem, e.g. sibling support, and perceived communication within the family, are of greater importance for the level of both participation attendance and the perceived importance of participating in domestic life and peer relations.

Conclusion: Everyday functioning in adolescents with self-reported neurodevelopmental impairments is partially affected by the same factors as for children without self-reported neurodevelopmental impairments. The effect of the neurodevelopmental impairment seems more evident in school and decreases in importance with age. Factors in the environment such as the experience of sibling support and communication patterns in the family must be taken into consideration when investigating influences on participation. When measuring participation both the frequency of attendance dimension as well as the perceived importance of the activity should be included as they seem to be related to partly differing influences.