https://doi.org/10.1177/1403494819893241 © Author(s) 2020 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/1403494819893241 journals.sagepub.com/home/sjp Scandinavian Journal of Public Health, 1–2 In his Letter to the Editor, Michiel Tack [1] addresses a concern that our reported prevalence of chronic fatigue syndrome (CFS) is misleading, as it is higher than in many other publications. We understand this concern, as it relates to some of the fundamental problems within the discipline of functional somatic disorders (FSD). First, we have multiple consensus- based definitions for each syndrome, some of which are developed in highly skewed samples and not vali- dated in general populations. Second, there is an urgent need for more valid (i.e. data-driven) pheno- typic approaches that can be used as the gold stand- ard for defining FSD. Third, in epidemiological research, we need broader symptom clusters that include both severely ill individuals but also those who have the syndrome in abbreviated or milder forms [2–5]. In light of these fundamental problems, DanFunD was initiated 10 years ago as a large-scale epidemio- logical study with the aim of unravelling the epidemi- ology of various FSD and diagnostic analogues [6]. In order to achieve this aim, we included standard criteria for five common syndromes, which: (1) were manageable and validated for use in large epidemiological studies on general populations (2) did not have symptom overlap (many definitions of CFS also include pain and various other symptoms) (3) allowed us to gain a genuine picture of the overlap of syndromes without the risk of obtaining an artificial overlap due to overlap of diagnostic criteria In order to maintain a broad and open-minded approach to FSD, DanFunD includes three different delimitations: first, a traditional diagnostic approach consisting of five common syndromes that we relieved from artificial overlap in diagnostic criteria (CFS being one of these); second, the unifying bodily dis- tress syndrome diagnostic construct; and third, eight symptom profiles [7]. We agree, however, that our obtained prevalence of 8.6% is high compared with other studies on CFS, and concur that this is easily explained by our use of a measure of severe fatigue for assigning case status of CFS. Consequently, one could argue that the reported prevalence describes the number of individuals with severe and abnormal fatigue rather than accounts for the number of individuals with CFS. This should have been described more clearly in the paper. We are aware of the limitations of using self-reported questionnaires as a case assignment method, as stated in the paper. We have approached this problem in another paper, currently in revision. Here, a diagnostic interview, performed by trained family physicians via telephone, was conducted with a stratified subsample Response to Letter to the Editor: A misleading CFS prevalence estimate in DanFunD MARIE WEINREICH PETERSEN 1 , ANDREAS SCHRöDER 1 , TORBEN JøRGENSEN 2,3,4 , EVA øRNBøL 1 , THOMAS MEINERTZ DANTOFT 2 , MARIE ELIASEN 2 , TINA WISBECH CARSTENSEN 1 , LENE FALGAARD EPLOV 5 & PER FINK 1 1 The Research Clinic for Functional Disorders and Psychosomatics, Aarhus University Hospital, Denmark, 2 Center for Clinical Research and Prevention, Bispebjerg and Frederiksberg Hospital, Denmark, 3 Department of Public Health, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark, 4 Faculty of Medicine, Aalborg University, Denmark, and, 5 Mental Health Centre Copenhagen, The Capital Region of Denmark, Denmark 893241SJP 0 0 10.1177/1403494819893241Scandinavian Journal of Public Health other 2020 Correspondence: Marie Weinreich Petersen, The Research Clinic for Functional Disorders and Psychosomatics, Aarhus University Hospital, Nørrebrogade 44, building 2C, 8000 Aarhus C, Denmark. E-mail: mawept@rm.dk