An illustration of data and explanatory models.

<p>(A) Prevalence of antidepressant purchases in divorced individuals in divorce-centred time (solid line) and in others in ordinary time (dashed line). The thick vertical line indicates the time of divorce. (B) The data points for model fitting and 95% Wald confidence intervals for prevalence; the general linear trend in non-divorced people and the baseline prevalence in divorced people was removed from prevalence data of the divorced individuals. (C) The stress-relief model (i.e. function <i>g</i>(<i>t</i>)) in the divorce-centred time t. (D) The stress-induction model. (E) The peak-stress model. (F) The adaptive model. Although all the model functions are shown here for illustration, their parametrisation is the one implied by the fitted models of the Results section.</p

Parameter estimates and fit statistics for the models.

<p>Parameter estimates and fit statistics for the models.</p

Possible state transitions in the evolutionary state-dependent model.

<p>Note that it is also possible to stay in the same state for longer than one time step, but for clarity the self-loops are not shown (but see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0179495#pone.0179495.s001" target="_blank">S1 Text</a>). A ‘strategy’ π(<i>x</i>,<i>t</i>) defines whether to be in a ‘depressed’ mode <i>u</i>₁ or not (mode <i>u</i>₀) given the state <i>x</i> and time <i>t</i>. The star superscript refers specifically to the optimal strategy that maximizes the reproductive value. The choice of mode dictates the transition-probability structure for the next time step. The effect of the ‘depressed’ mode is to decrease the probability of a divorce-like transition from the relationship-at-risk state to the unpartnered state by the value <i>s</i>, to increase the probability of death <i>m</i> by <i>z</i>, and to remove the probability of marrying <i>ρ</i> (removal of <i>ρ</i> had no consequences here, but to some, it seems a logical outcome of depression). We assumed that as many relationships at risk end up in divorce as in reconciliation on average (<i>d</i>₂); the function <i>f</i>(<i>d</i>₁, <i>d</i>₂) captured the overall divorce rate, as illustrated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0179495#pone.0179495.s001" target="_blank">S1 Text</a>.</p

Sensitivity analysis using SSRI data.

<p>(A) Prevalence of selective serotonin reuptake inhibitor (SSRI; solid lines) and tricyclic antidepressants (TCA; dashed lines) purchases in divorced (d; thick lines) and non-divorced (nd; thin lines) individuals. Time is centred around the divorce for the divorcees. (B) Fit of the stress-relief model (line) to the SSRI data points (circles). (C) Fit of the peak-stress model. (D) Fit of the adaptive model.</p

Model estimates compared with the data.

<p>(A) The stress-relief model. (B) The stress-induction model. (C) The peak-stress model. (D) The adaptive model. Solid lines show the model of interest, whereas the dashed line illustrates what would happen in the adaptive model if depressive episodes would imply roughly 15 times the mortality compared to the model of interest (<i>m</i> + <i>z</i>, with <i>z</i> = 0.06, rather than <i>m</i> + <i>z</i>, with <i>z</i> = 0.0024); in that case, the depressed mode of behaving would no longer be adaptive under any circumstances.</p