Psychosocial and sociodemographic predictors of attrition in a longitudinal study of major depression in primary care: the predictD-Spain study.
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.
Bellón
Juan Angel
JA
Departamento de Medicina Preventiva, Facultad de Medicina, Universidad de Málaga, Campus de Teatinos, Málaga 29071, Spain. jabellon@terra.es
de Dios Luna
Juan
J
Moreno
Berta
B
Montón-Franco
Carmen
C
GildeGómez-Barragán
María Josefa
MJ
Sánchez-Celaya
Marta
M
Díaz-Barreiros
Miguel Angel
MA
Vicens
Catalina
C
Motrico
Emma
E
Martínez-Cañavate
María Teresa
MT
Oliván-Blázquez
Bárbara
B
Vázquez-Medrano
Ana
A
Sánchez-Artiaga
María Soledad
MS
March
Sebastiá
S
del Mar Muñoz-García
María
M
Moreno-Peral
Patricia
P
Nazareth
Irwin
I
King
Michael
M
Torres-González
Francisco
F
D000293:Adolescent; D000328:Adult; D000368:Aged; D003865:Major Depressive Disorder / Q000175:diagnosis / Q000453:epidemiology / Q000523:psychology*; D005260:Female; D005500:Follow-Up Studies; D015438:Health Behavior; D006801:Humans; D016015:Logistic Models; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D011594:Psychometrics; D045808:Refusal to Participate / Q000523:psychology* / Q000706:statistics & numerical data; D012307:Risk Factors; D012923:Social Class; D013030:Spain / Q000453:epidemiology; D011795:Surveys and Questionnaires; D055815:Young Adult