While the effect of anxiety and depression on FSS is strong and immediate, FSS exert a weaker and delayed influence on anxiety and depression. Further research should be done to detect the exact ways in which anxiety and depression lead to FSS, and FSS lead to anxiety and depression.

BackgroundElectronic diaries are increasingly used in diverse disciplines to collect momentary data on experienced feelings, cognitions, behavior and social context in real life situations. Choices to be made for an effective and feasible design are however a challenge. Careful and detailed documentation of argumentation of choosing a particular design, as well as general guidelines on how to design such studies are largely lacking in scientific papers. This qualitative study provides a systematic overview of arguments for choosing a specific diary study design (e.g. time frame) in order to optimize future design decisions.MethodsDuring the first data assessment round, 47 researchers experienced in diary research from twelve different countries participated. They gave a description of and arguments for choosing their diary design (i.e., study duration, measurement frequency, random or fixed assessment, momentary or retrospective assessment, allowed delay to respond to the beep). During the second round, 38 participants (81%) rated the importance of the different themes identified during the first assessment round for the different diary design topics.ResultsThe rationales for diary design choices reported during the first round were mostly strongly related to the research question. The rationales were categorized into four overarching themes: nature of the variables, reliability, feasibility, and statistics. During the second round, all overarching themes were considered important for all diary design topics.ConclusionsWe conclude that no golden standard for the optimal design of a diary study exists since the design depends heavily upon the research question of the study. The findings of the current study are helpful to explicate and guide the specific choices that have to be made when designing a diary study.Electronic supplementary materialThe online version of this article (10.1186/s12874-018-0579-6) contains supplementary material, which is available to authorized users.

Parental overprotection may play a role in the development of FSS in young adolescents.

Functional limitations in FSS patients are common, and as severe as those in patients with MD when looking at QoL and work participation, emphasizing that FSS are serious health conditions.

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Mood and anxiety disorders are more prevalent in individuals with FSSs, and particularly CFS, than in individuals without FSSs. However, most individuals with FSSs do not have mood or anxiety disorders.

WHAT'S KNOWN ON THIS SUBJECT:Functional somatic symptoms, such as overtiredness and pain, are more common in girls than in boys, and this difference tends to increase during adolescence. Whether this increase in gender difference can be explained by pubertal development is unclear. WHAT THIS STUDY ADDS:Two large cohort studies in the Netherlands and the United States revealed no significant gender differences in the association between pubertal development and functional somatic symptoms. Pubertal stage at baseline positively predicted back pain, overtiredness, and dizziness at follow-up. abstract OBJECTIVE: Functional somatic symptoms, symptoms for which no organic pathologic basis can be found, are more prevalent in girls than in boys, and this difference tends to increase during adolescence. This might be explained, at least in part, by pubertal development. We hypothesized that pubertal maturation predicts the development of most functional somatic symptoms and that this especially is true for girls. METHOD:We used 2 longitudinal population-based studies to examine our hypotheses: the Longitudinal Study of Pain in Adolescents in Seattle (n ϭ 1996 [49.7% girls]) and the Dutch Tracking Adolescents' Individual Lives Survey (n ϭ 2230 [51.0% girls]). Two assessment waves of each study were used. American adolescents were younger than Dutch adolescents at the first (11.6 vs 13.6) and second (14.5 vs 16.2) assessment waves, but they were in about the same pubertal development stage. Functional somatic symptoms were measured by pain questions, the Symptom Checklist-90, and the Youth Self-report. The Pubertal Development Scale was used to assess pubertal development on a continuous scale in both cohorts. RESULTS:Ordinal logistic regression analyses revealed that American and Dutch adolescents at a later pubertal status at baseline were more likely (odds ratios ranged from 1.24 to 1.61) to report back pain, overtiredness, and dizziness but not stomach pain and headache 2 to 3 years later. Although these relationships were not equally strong for boys and girls, no significant gender differences were found. CONCLUSIONS:Pubertal status predicted the frequency of some, but not all, functional somatic symptoms at follow-up. Pediatrics 2011;128: 553-559

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