Our outcome-based definition of resilience has consequences for operationalization. If resilience is the outcome of a process and not a stable individual characteristic or trait, then resilience cannot be measured at any time point before or during stressor exposure with a questionnaire, a gene test, a brain scan, or other one-time assessments. Instead, resilience requires a measurement of mental health at at least two time points: before and some time after stressor exposure. Only this allows for observing potential changes in mental health status as a result of stressor exposure. Ideally, mental health is monitored more frequently and also over some time after the end of stressor exposure, to be able to delineate mental health trajectories (and hence the process of adaptation) at better temporal resolution and to safely constate a stable, long-term mental health outcome.
Because resilience is defined as mental health despite adversity, resilience studies necessarily also need to quantify adversity, i.e., the individual’s exposure to stressor(s). Only by relating changes in somebody’s mental health to that person’s stressor load, one can say if a person is resilient – staying healthy in the absence of stressors is not resilience, and showing a degree X of impairment due to some stressor S1 is a more resilient outcome than showing the same degree X of impairment after a weaker stressor S2.
The measurement of adversity (i.e., the stressors subjects are exposed to) will be the more precise the less time has elapsed between stressor exposure and measurement. Closely spaced stressor measurements in real time or with only short intervals of retrospection are preferable.
Hence, measuring resilience needs at least two things: a measure of mental health and a measure of stressor exposure, and mental health needs to be measured at least at two time points. Where measuring mental health before stressor exposure is technically not possible (such as can be the case in disaster studies), the assumption of comparable mental health before stressor exposure in the study participants has to be clearly marked as a limitation, or researchers have to report a control group not exposed to the stressor in question, but otherwise comparable to the stressed group.