In the HUNT studies in Norway from the 1990s the prevalence was 1% in adults [24] and 0.5% in adolescents [25], whereas a more recent study showed 1.7%[26]].
Despite this, the wide scope of the HUNT studies (they addressed a broad range of medical disorders) made biases with relevance to headache or RA unlikely.
The Norwegian Data Inspectorate, the Norwegian Board of Health, and the Regional Committee for ethics in Medical Research had approved all HUNT studies, and the Regional Committee also approved the present analysis.
The 1006 participants were 50-65 yeats at inclusion, had participated in all previous HUNT studies (1, 2 and 3), and had been randomly selected to a population-based imaging study of the head (MRI-HUNT, 2007-2009).
Despite this limitation, the HUNT studies include more than 200 health related variables, which will probably ensure that any remaining bias relevant to insomnia, headache and CMSCs is negligible.
The reference group consisted of age-matched men from the HUNT studies (controls).
The HUNT studies have been approved by the Regional Committee for Medical and Health Research Ethics, Central Norway and the Norwegian Data Inspectorate.
The HUNT studies are generally regarded as a survey of 'Mini-Norway'.
The HUNT studies are approved by the Data Inspectorate of Norway and by the Regional Committee for Medical Research Ethics.
General well-being is a five-item quality of life scale validated in earlier HUNT studies.
The results are based upon two consecutive public health studies conducted within the county of Nord-Trøndelag Nord-Trøndelag, Norwayies).
