J Epidemiol Community Health 64:874-884 doi:10.1136/jech.2008.085290
  • Research report

Psychosocial and sociodemographic predictors of attrition in a longitudinal study of major depression in primary care: the predictD-Spain study

  1. Francisco Torres-González13
  1. 1Centro de Salud El Palo, Unidad de Investigación del Distrito de Atención Primaria de Málaga (redIAPP, grupo SAMSERAP), Departamento de Medicina Preventiva, Universidad de Málaga, Spain
  2. 2Departamento de Bioestadística (redIAPP, grupo SAMSERAP), Universidad de Granada, Spain
  3. 3Fundación IMABIS, Unidad de Investigación del Distrito de Atención Primaria de Málaga (redIAPP, grupo SAMSERAP), Facultad de Psicología. Universidad de Málaga, Spain
  4. 4Centro de Salud Casablanca (redIAPP, grupo Aragón), Departamento de Medicina y Psiquiatría, Universidad de Zaragoza, Spain
  5. 5Unidad Docente de Medicina Familiar y Comunitaria de La Rioja, Servicio Riojano de la Salud, Logroño, La Rioja, Spain
  6. 6Unidad Docente de Medicina Familiar y Comunitaria, Área I de Atención Primaria, Madrid, Spain
  7. 7Centro de Salud Vecindario, Gerencia de Atención Primaria de Gran Canaria, Servicio Canario de Salud, Las Palmas, Spain
  8. 8Centro de Salud son Serra-La Vileta, Unidad Docente de Medicina Familiar y Comunitaria de Mallorca, Instituto Balear de la Salud (redIAPP, grupo Baleares), Palma de Mallorca, Illes Balears, Spain
  9. 9Fundación IAVANTE, Granada, Spain
  10. 10Unidad de Investigación de Atención Primaria (redIAPP, grupo Aragón), Instituto Aragonés de Ciencias de la Salud, Zaragoza, Spain
  11. 11Centro de Salud Condes de Barcelona-Boadilla, Área 6 de Atención Primara, Madrid, Spain
  12. 12Unidad de Investigación de Atención Primaria de Baleares (redIAPP, grupo Baleares), Mallorca, Spain
  13. 13Grupo Andaluz de Investigación en Salud Mental, Departamento de Psiquiatría y Medicina legal, Universidad de Granada, Spain
  14. 14Medical Research Council General Practice Research Framework, London, UK
  15. 15Department of Mental Health Sciences, University College London, London, UK
  1. Correspondence to Juan Ángel Bellón, Departamento de Medicina Preventiva, Facultad de Medicina, Universidad de Málaga, Campus de Teatinos, Málaga 29071, Spain; jabellon{at}
  1. Contributors JAB is guarantor for the predictD-Spain study. JAB, BM, FT-G and CM-F obtained funding for implementing the study in Spain. JAB coordinated the predictD-Spain study. BM-K, FG-T, CM-F, MJGdG-B, MS-C, MAD-B and CV coordinated the study in each Spanish province. MTM-C, BO-B, AV-M, MSS-A, SM, EM-M, MMM-G and PM-P collaborated implementing the study in each province. MK and IN developed the idea and obtained funding for the predictD International study. JDL collaborated in the design, and JAB and JDL analysed the data. JAB drafted the paper and all authors agreed the final version.

  • Accepted 17 August 2009
  • Published Online First 16 September 2009


Background Few data exist on the psychosocial factors associated with attrition in longitudinal surveys. This study was undertaken to determine psychosocial and sociodemographic predictors of attrition from a longitudinal study of the onset and persistence of episodes of major depression in primary care.

Methods A systematic random sample of general practice attendees was recruited in seven Spanish provinces between October 2005 and February 2006. Major depression was diagnosed using the Composite International Diagnostic Interview and a set of 39 individual and environmental risk factors for depression were assessed at baseline and after 6 and 12 months of follow-up. Data were analysed using multilevel logistic regression.

Results 7777 primary care attendees aged 18–75 years were selected, of whom 1251 (16.1%) were excluded. Of the remaining 6526, 1084 (16.6%) refused to participate. Thus, 5442 patients (attending 231 family physicians in 41 health centres) were interviewed at baseline, of whom 3804 (70%) and 3567 (66%) remained at 6 and 12 months of follow-up, respectively. The province and sociodemographic factors were stronger predictors of attrition than psychosocial factors. Depression and anxiety had no effect but other psychosocial factors affected attrition. There were different profiles for the patients lost at 12 months when predictors measured at baseline versus 6 months were included.

Conclusions These findings suggest that several psychosocial factors might be considered factors of attrition in primary care cohorts and confirm that baseline characteristics are insufficient for analysing non-response in longitudinal studies, indicating that different retention strategies should be applied for patients interviewed at 6 and 12 months.


  • Funding This work was supported in Spain by grants from the Spanish Ministry of Health (grant FIS references: PI041980, PI041771, PI042450 and PI06/1442); the Andalusian Council of Health (grant references: 05/403 and 06/278); the Spanish Network of Primary Care Research ‘redIAPP’ (RD06/0018), the ‘Aragón group’ (RD06/0018/0020), the ‘Baleares group’ (RD07/0018/0033) and the ‘SAMSERAP group’ (RD06/0018/0039). The Malaga sample, as part of the predictD-International study, was also co-funded by a grant from The European Commission (reference QL4-CT2002-00683).

  • Competing interests None.

  • Ethics approval Ethical approval for the study was obtained from the relevant ethics committees.

  • Provenance and peer review Not commissioned; externally peer reviewed.