Cambridge University Press



Supplementary material S2Categorization of variables included in the attrition analysesThe following sociodemographic- and health-related data obtained from the Danish registers ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1177/1403494811399956 [doi]","ISSN":"1651-1905; 1403-4948","abstract":"Danish registers contain information on many important health and social issues. Because all Danish citizens have a unique personal identification number, linkage at the individual level between these nationwide registers and other data sources is possible and feasible. In this paper we briefly introduce selected Danish registers and the data structure and requirements forgetting access to data at Statistics Denmark, which is the main provider of register data. We introduce the Danish Data Archive and briefly present the Act on Processing of Personal Data, which is the legal foundation for analyses of register-based data in Denmark.","author":[{"dropping-particle":"","family":"Thygesen","given":"L C","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Daasnes","given":"C","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Thaulow","given":"I","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Bronnum-Hansen","given":"H","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Scandinavian Journal of Public Health","id":"ITEM-1","issue":"7 Suppl","issued":{"date-parts":[["2011","7"]]},"note":"LR: 20170214; JID: 100883503; 2011/09/08 06:00 [entrez]; 2011/09/08 06:00 [pubmed]; 2011/09/29 06:00 [medline]; ppublish","page":"12-16","publisher-place":"National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark. lct@niph.k","title":"Introduction to Danish (nationwide) registers on health and social issues: structure, access, legislation, and archiving","type":"article-journal","volume":"39"},"uris":[""]},{"id":"ITEM-2","itemData":{"ISSN":"1403-4948","abstract":"BACKGROUNDThe Danish National Patient Register (NPR) was established in 1977, and it is considered to be the finest of its kind internationally.BACKGROUNDAt the onset the register included information on inpatient in somatic wards. The content of the register has gradually been expanded, and since 2007 the register has included information on all patients in Danish hospitals.RESULTSAlthough the NPR is overall a sound data source, both the content and the definitions of single variables have changed over time. Changes in the organisation and provision of health services may affect both the type and the completeness of registrations.CONCLUSIONSThe NPR is a unique data source. Researchers using the data should carefully consider potential fallacies in the data before drawing conclusions.","author":[{"dropping-particle":"","family":"Lynge","given":"E","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Sandegaard","given":"J L","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Rebolj","given":"M","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Scandinavian Journal of Public Health","id":"ITEM-2","issue":"7","issued":{"date-parts":[["2011"]]},"page":"30-33","publisher-place":"Sweden DOI - 10.1177/1403494811401482","title":"The Danish National Patient Register","type":"article-journal","volume":"39"},"uris":[""]},{"id":"ITEM-3","itemData":{"DOI":"10.1093/ije/dyw213","ISSN":"0300-5771","PMID":"27789670","author":[{"dropping-particle":"","family":"Potteg?rd","given":"A","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Schmidt","given":"SAJ","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wallach-Kildemoes","given":"H","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"S?rensen","given":"HT","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Hallas","given":"J","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Schmidt","given":"M","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"International journal of epidemiology","id":"ITEM-3","issue":"3","issued":{"date-parts":[["2017","6","1"]]},"page":"798","title":"Data Resource Profile: The Danish National Prescription Registry.","type":"article-journal","volume":"46"},"uris":[""]},{"id":"ITEM-4","itemData":{"ISSN":"0393-2990","abstract":"The methodological advances in epidemiology have facilitated the use of the Danish Civil Registration System (CRS) in ways not previously described systematically. We reviewed the CRS and its use as a research tool in epidemiology. We obtained information from the Danish Law on Civil Registration and the Central Office of Civil Registration, and used existing literature to provide illustrative examples of its use. The CRS is an administrative register established on April 2, 1968. It contains individual-level information on all persons residing in Denmark (and Greenland as of May 1, 1972). By January 2014, the CRS had cumulatively registered 9.5 million individuals and more than 400 million person-years of follow-up. A unique ten-digit Civil Personal Register number assigned to all persons in the CRS allows for technically easy, cost-effective, and unambiguous individual-level record linkage of Danish registers. Daily updated information on migration and vital status allows for nationwide cohort studies with virtually complete long-term follow-up on emigration and death. The CRS facilitates sampling of general population comparison cohorts, controls in case-control studies, family cohorts, and target groups in population surveys. The data in the CRS are virtually complete, have high accuracy, and can be retrieved for research purposes while protecting the anonymity of Danish residents. In conclusion, the CRS is a key tool for epidemiological research in Denmark.","author":[{"dropping-particle":"","family":"Schmidt","given":"M","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Pedersen","given":"L","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"S?rensen","given":"H T","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"European journal of epidemiology","id":"ITEM-4","issue":"8","issued":{"date-parts":[["2014"]]},"page":"541-549","publisher-place":"Netherlands DOI - 10.1007/s10654-014-9930-3","title":"The Danish Civil Registration System as a tool in epidemiology","type":"article-journal","volume":"29"},"uris":[""]},{"id":"ITEM-5","itemData":{"ISSN":"1403-4948","abstract":"BACKGROUNDThe Psychiatric Central Research Register (PCRR) has continued since 1970 with electronic registration of patients treated at psychiatric departments in Denmark.BACKGROUNDThe register contains dates of onset and end of any treatment; all diagnoses; type of referral; place of treatment; municipality of residence; mode of admission.RESULTSSystematic studies validating the clinical diagnoses do not exist. However, several studies have validated specific diagnoses. The nationwide registration of severe mental disorders is almost complete. However, most cases with mild to moderate mental disorders are diagnosed and treated by general practitioners or specialists in psychiatry working in private practice and are thus not registered in the PCRR.CONCLUSIONSThe PCRR is a valuable tool in national health planning and in epidemiological research.","author":[{"dropping-particle":"","family":"Mors","given":"O","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Perto","given":"G P","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mortensen","given":"P B","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Scandinavian Journal of Public Health","id":"ITEM-5","issue":"7","issued":{"date-parts":[["2011"]]},"page":"54-57","publisher-place":"Sweden DOI - 10.1177/1403494810395825","title":"The Danish Psychiatric Central Research Register","type":"article-journal","volume":"39"},"uris":[""]}],"mendeley":{"formattedCitation":"(1–5)","plainTextFormattedCitation":"(1–5)","previouslyFormattedCitation":"(1–5)"},"properties":{"noteIndex":0},"schema":""}(1–5) are included in the attrition analysis and categorized as follows; Age and sex (The Danish Civil Registration System): at the time the first invitation for the survey were sent.Marital status (The Danish Civil Registration System): categorized binary as married/cohabiting or single.Educational level (Registers on personal level of education): Lower secondary school; Upper secondary school; Vocational or short-cycle higher education; Medium-cycle higher education including bachelor; Long-cycle higher education; Missing. Occupation status (Registers on personal labor market affiliation): In the labor force; Unemployment, sick pay and leave of absence; Disability pension and social security benefit; Retirement pension, early; Enrolled in education, and Missing.Personal income (The Income Statistics Register): Used for the adult populations. The categorizing is based on the general population’s income divided into quintiles: < 21,906 euro; 21,906 euro – 38,145 euro; 38,146 euro – 48,914 euro; 48,915 euro – 63,329 euro; >63,329 euro. Missing.The equivalated disposable income (The Income Statistics Register): Used for the adolescent population. The purpose of using this variable is to ensure comparability in income by taking both the size- and total income of a family into account.The categorizing will be based on the equivalated disposable income for the general population divided into quintiles.Degree of urbanization (The Danish Civil Registration System): Densely populated; Intermediately populated, largest town ≥ 40,000 inhabitants; Intermediately populated, largest town < 40,000 inhabitants; Intermediately populated, largest town < 15,000 inhabitants; Thinly populated, largest town ≥ 15,000 inhabitants; Thinly populated, largest town < 15,000 inhabitants.Geography/region (The Danish Civil Registration System): Capital, Central part of Jutland, Northern part of Jutland, Zealand, Southern part of Denmark.Prior mental disorder (The Psychiatric Central Research Register): defined as any contact (both in- and outpatient) with a psychiatric hospital registered in the Psychiatric Central Research Register ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"ISSN":"1403-4948","abstract":"BACKGROUNDThe Psychiatric Central Research Register (PCRR) has continued since 1970 with electronic registration of patients treated at psychiatric departments in Denmark.BACKGROUNDThe register contains dates of onset and end of any treatment; all diagnoses; type of referral; place of treatment; municipality of residence; mode of admission.RESULTSSystematic studies validating the clinical diagnoses do not exist. However, several studies have validated specific diagnoses. The nationwide registration of severe mental disorders is almost complete. However, most cases with mild to moderate mental disorders are diagnosed and treated by general practitioners or specialists in psychiatry working in private practice and are thus not registered in the PCRR.CONCLUSIONSThe PCRR is a valuable tool in national health planning and in epidemiological research.","author":[{"dropping-particle":"","family":"Mors","given":"O","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Perto","given":"G P","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Mortensen","given":"P B","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Scandinavian Journal of Public Health","id":"ITEM-1","issue":"7","issued":{"date-parts":[["2011"]]},"page":"54-57","publisher-place":"Sweden DOI - 10.1177/1403494810395825","title":"The Danish Psychiatric Central Research Register","type":"article-journal","volume":"39"},"uris":[""]}],"mendeley":{"formattedCitation":"(5)","plainTextFormattedCitation":"(5)","previouslyFormattedCitation":"(5)"},"properties":{"noteIndex":0},"schema":""}(5) in the period from 1969 and forth. The listed ICD-10 diagnosis (Classification of Mental and Behavioural Disorders) ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"author":[{"dropping-particle":"","family":"World Health Organization Geneva","given":"","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["1993"]]},"title":"The ICD-10 Classification of Mental and Behavioural Disorders - Diagnostic criteria for research","type":"book"},"uris":[""]}],"mendeley":{"formattedCitation":"(6)","plainTextFormattedCitation":"(6)","previouslyFormattedCitation":"(6)"},"properties":{"noteIndex":0},"schema":""}(6), (before 1993 the corresponding ICD-8 diagnosis), for the hospital contact were used. The following diagnostic groups were defined: Mental and behavioral disorders due to psychoactive substance use (F10-F19); Psychotic disorders (F20-F29); Mood disorders (F30-F33); Anxiety disorders incl. Obsessive-compulsive disorder, Post-traumatic stress disorder (F40-F42, F431); Eating disorders (F50); Personality Disorders (F60-F62.1); Pervasive developmental disorders incl. autism (F84.0, F84.1, F84.5, F84.8); Behavioral and emotional disorders incl. ADHD (F90, F90.1, F90.8, F98.8); Any other mental disorder (not included in the defined diagnostic groups). Each individual may be present in more than one category – if he or she has more than one diagnosis. Use of psychotropic medication (The National Prescription Register), as registered in the National Prescription Register ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1093/ije/dyw213","ISSN":"0300-5771","PMID":"27789670","author":[{"dropping-particle":"","family":"Potteg?rd","given":"A","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Schmidt","given":"SAJ","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wallach-Kildemoes","given":"H","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"S?rensen","given":"HT","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Hallas","given":"J","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Schmidt","given":"M","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"International journal of epidemiology","id":"ITEM-1","issue":"3","issued":{"date-parts":[["2017","6","1"]]},"page":"798","title":"Data Resource Profile: The Danish National Prescription Registry.","type":"article-journal","volume":"46"},"uris":[""]}],"mendeley":{"formattedCitation":"(3)","plainTextFormattedCitation":"(3)","previouslyFormattedCitation":"(3)"},"properties":{"noteIndex":0},"schema":""}(3), which contains data from 1995 and onwards. The following groups of medication were used (Anatomical Therapeutic Chemical (ATC) codes in parentheses): Antipsychotics (N05A - N05AX17 excl. N05AN); Lithium (N05AN); Anxiolytics (N05BA*, N05CD02, N05CD05, N05CD06, N03AX16); Antidepressants (N06A - N06AX26); Attention Deficit Hyperactivity Disorder medication (N06BA09, N06BA04, N06BA12, N06BA02, C02AC02, N06BA07); Medication for addiction disorders (N07BB*, N07BC*). Each individual may be present in more than one category – if he or she has been prescribed more than one category of psychotropic medication.Somatic comorbidity (The National Patient Register): as measured by the Charlson Comorbitity Index ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1016/0021-9681(87)90171-8","ISSN":"0021-9681","PMID":"3558716","abstract":"The objective of this study was to develop a prospectively applicable method for classifying comorbid conditions which might alter the risk of mortality for use in longitudinal studies. A weighted index that takes into account the number and the seriousness of comorbid disease was developed in a cohort of 559 medical patients. The 1-yr mortality rates for the different scores were: \"0\", 12% (181); \"1-2\", 26% (225); \"3-4\", 52% (71); and \"greater than or equal to 5\", 85% (82). The index was tested for its ability to predict risk of death from comorbid disease in the second cohort of 685 patients during a 10-yr follow-up. The percent of patients who died of comorbid disease for the different scores were: \"0\", 8% (588); \"1\", 25% (54); \"2\", 48% (25); \"greater than or equal to 3\", 59% (18). With each increased level of the comorbidity index, there were stepwise increases in the cumulative mortality attributable to comorbid disease (log rank chi 2 = 165; p less than 0.0001). In this longer follow-up, age was also a predictor of mortality (p less than 0.001). The new index performed similarly to a previous system devised by Kaplan and Feinstein. The method of classifying comorbidity provides a simple, readily applicable and valid method of estimating risk of death from comorbid disease for use in longitudinal studies. Further work in larger populations is still required to refine the approach because the number of patients with any given condition in this study was relatively small.","author":[{"dropping-particle":"","family":"Charlson","given":"M E","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Pompei","given":"P","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Ales","given":"K L","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"MacKenzie","given":"C R","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Journal of chronic diseases","id":"ITEM-1","issue":"5","issued":{"date-parts":[["1987"]]},"page":"373-83","title":"A new method of classifying prognostic comorbidity in longitudinal studies: development and validation.","type":"article-journal","volume":"40"},"uris":[""]}],"mendeley":{"formattedCitation":"(7)","plainTextFormattedCitation":"(7)","previouslyFormattedCitation":"(7)"},"properties":{"noteIndex":0},"schema":""}(7) based on hospital contacts (both in- and outpatients) registered in the Danish National Patient Register ADDIN CSL_CITATION {"citationItems":[{"id":"ITEM-1","itemData":{"ISSN":"1403-4948","abstract":"BACKGROUNDThe Danish National Patient Register (NPR) was established in 1977, and it is considered to be the finest of its kind internationally.BACKGROUNDAt the onset the register included information on inpatient in somatic wards. The content of the register has gradually been expanded, and since 2007 the register has included information on all patients in Danish hospitals.RESULTSAlthough the NPR is overall a sound data source, both the content and the definitions of single variables have changed over time. Changes in the organisation and provision of health services may affect both the type and the completeness of registrations.CONCLUSIONSThe NPR is a unique data source. Researchers using the data should carefully consider potential fallacies in the data before drawing conclusions.","author":[{"dropping-particle":"","family":"Lynge","given":"E","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Sandegaard","given":"J L","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Rebolj","given":"M","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Scandinavian Journal of Public Health","id":"ITEM-1","issue":"7","issued":{"date-parts":[["2011"]]},"page":"30-33","publisher-place":"Sweden DOI - 10.1177/1403494811401482","title":"The Danish National Patient Register","type":"article-journal","volume":"39"},"uris":[""]}],"mendeley":{"formattedCitation":"(2)","plainTextFormattedCitation":"(2)","previouslyFormattedCitation":"(2)"},"properties":{"noteIndex":0},"schema":""}(2) since 1977. The listed ICD-10 diagnosis (before 1993 the corresponding ICD-8 diagnosis) for the hospital contact were used. The total Charlson Comorbidity Index score were categorized in: 0 no comorbidity; 1-2 moderate comorbidity; and 3 or more as high/severe comorbidity. References:ADDIN Mendeley Bibliography CSL_BIBLIOGRAPHY 1. Thygesen LC, Daasnes C, Thaulow I, Bronnum-Hansen H. Introduction to Danish (nationwide) registers on health and social issues: structure, access, legislation, and archiving. Scand J Public Health. 2011;39(7 Suppl):12–16.2. Lynge E, Sandegaard JL, Rebolj M. The Danish National Patient Register. Scand J Public Health. 2011;39(7):30–33.3. Potteg?rd A, Schmidt S, Wallach-Kildemoes H, S?rensen H, Hallas J, Schmidt M. Data Resource Profile: The Danish National Prescription Registry. Int J Epidemiol. 2017;46(3):798.4. Schmidt M, Pedersen L, S?rensen HT. The Danish Civil Registration System as a tool in epidemiology. Eur J Epidemiol. 2014;29(8):541–549.5. Mors O, Perto GP, Mortensen PB. The Danish Psychiatric Central Research Register. Scand J Public Health. 2011;39(7):54–57.6. World Health Organization Geneva. The ICD-10 Classification of Mental and Behavioural Disorders - Diagnostic criteria for research. 1993.7. Charlson ME, Pompei P, Ales KL, MacKenzie CR. A new method of classifying prognostic comorbidity in longitudinal studies: development and validation. J Chronic Dis. 1987;40(5):373–83. ................
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