The data used in this study is derived from eight patients
with bipolar disorder whose mood was monitored over
a period of 5 years. The mood data is returned approximately
each week and comprises answers to standard
self-rating questionnaires for depression and mania. We
restrict the investigation to the depression data which
is more amenable to analysis than mania: for some
patients, the mania scores are at or near zero for the
period of monitoring. The rating scale used for depression
is the Quick Inventory of Depressive Symptomatology -
Self Report (QIDS-SR16) (Rush et al. 2000) which covers
nine symptom domains for depression (DSM-IV-TR)
(American Psychiatric Association 2000). This scale has
been evaluated for psychometric properties and found to
have high validity (Rush 2003). Each domain can contribute
up to 3 points giving a total possible score of 27
on the scale. Details of the selection process are given in
Additional file 1: Section I and plots of the selected time
series are shown in Figure 1.