Study sample and statistical analysis
Of the 10 308 respondents who participated in the baseline
screening of the Whitehall II study 8629 (83%) participated in
Phase 4 and 7824 (76%) at Phase 5. The 3685 participants eligible
for inclusion in this paper were those in civil service
employment at Phase 4 who were still working at Phase 5. Of
these, 3360 responded to the job insecurity item in both the
Phase 4 and Phase 5 questionnaires, 931 women and 2429
men.
The aim of the analysis was to compare self reported health,
minor psychiatric morbidity, physiological measures, and
health related behaviours at Phase 5 for participants whose
job had remained secure (control group) with those for three
exposure groups; participants who had lost or gained job
security between Phases 4 and 5, and participants whose jobs
were insecure at both time points (chronic insecurity).
For continuous variables, differences in self reported health,
minor psychiatric morbidity, physiological measures, and
health related behaviours at Phase 5 between participants in
the exposure groups and those in the control group were
assessed using analysis of covariance. Adjusted means and
standard errors for all groups were produced by linear
regression (GLM procedure in SAS). Results for continuous
variables are presented by comparing the exposure group with
the control group in terms of adjusted mean differences (Adj
Diff) for the variable of interest and the standard error (SE) of
the mean difference. For dichotomous variables, logistic
regression (LOGIST in SAS) was used to compare Phase 5 self
reported health, minor psychiatric morbidity, physiological
measures, and health related behaviours in all groups. Results
for the dichotomous variables are presented in terms of odds