Sense of coherence and attrition during four-year follow-up in cohorts of permanent and non-permanent Finnish employees.
BACKGROUND
We studied whether health resources, measured as sense of coherence (SOC), are associated with participation in a follow-up survey among permanent and non-permanent employees who responded at baseline.


METHODS
Of a cohort of 5,981 permanent employees, those who after four years were still in the service of the same employer were asked to participate in a follow-up survey. Another cohort consisted of 2,194 fixed-term and 682 subsidised employees; among these the follow-up survey was posted to those whose addresses were found in the population register. Non-participation was divided into loss to follow-up (i.e., failure to locate the individual, death and, among permanent employees, turnover or exit from labour market) and non-response to the follow-up survey. Logistic regression analyses were used to examine whether the respondents differed from the non-respondents with respect to SOC and other characteristics at baseline.


RESULTS
Among permanent employees the follow-up survey yielded 3,998 respondents, 1,051 were lost, and 932 did not reply. Among non-permanent employees the follow-up survey yielded 1,563 respondents on initially fixed-term and 467 on subsidised contracts, the corresponding figures for those lost were 145 and 38, and for the non-respondents 486 and 177. Low SOC was associated with lower response rate among fixed-term but not among permanent or subsidised employees. No association was found between SOC and loss to follow-up.


CONCLUSIONS
SOC is a potential source of non-random sample attrition and should be taken into account for when estimating bias due to non-participation in occupational cohorts that include fixed-term employees.
Liukkonen
Virpi
V
Tampere School of Public Health, FIN-33014 University of Tampere, Finland. virpi.liukkonen@uta.fi
Virtanen
Pekka
P
Kivimäki
Mika
M
Pentti
Jaana
J
Vahtera
Jussi
J
D000293:Adolescent; D000328:Adult; D004651:Employment / Q000706:statistics & numerical data*; D005260:Female; D005387:Finland; D005500:Follow-Up Studies; D006801:Humans; D007389:Internal-External Control; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D008960:Models, Psychological; D016017:Odds Ratio; D010559:Personnel Management; D012649:Self Concept