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Table 8 The effect of considering indirectness when judging quality of evidence

From: Judging the quality of evidence in reviews of prognostic factor research: adapting the GRADE framework

Factor Example
Indirectness in population In our review we were interested in all headache sufferers. There were three longitudinal studies in the literature that examined the type of headache (that is, migraine or tension-type) as a prognostic factor for headache persistence [24, 30, 31]. All three studies recruited participants from headache clinics. These populations are not representative of all headache sufferers in the general population. It is likely that only those with more severe and frequent headache conditions are referred to a headache specialist [32]. We therefore downgraded the body of evidence on type of headache as a prognostic factor of headache persistence for serious indirectness.
Indirectness in prognostic factor We cannot provide examples extracted from our review since our review was not intentionally limited to a specific prognostic factor. Instead our goal has been to explore all types of factors that have been investigated to date as potential risk or protective factors for the persistence of a variety of chronic pain conditions and their associated disability. However, this poor representation would happen, for example, if we were interested in exploring the effect of mental illnesses on the persistence of recurrent headaches and the primary studies included were only investigating the prognostic value of depression diagnosis on onset of headaches.
Indirectness in outcome For example, this poor representation of outcome would happen if we were interested in exploring whether race is a risk factor for the persistence of recurrent headaches and the outcome was represented by studies assessing only the persistence of migraine (and at least not all types of the main primary headache disorders).