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Experiences or conditions threatening relevant development, safety or functioning. Adversity exposure should be characterized by nature, severity, duration, timing and context rather than assumed identical across people with the same event count. Objective circumstances and their subjective appraisal provide different information.

Adversity exposure is a person's history of experiences or conditions classified as adversity under a stated research definition. Event type, severity, duration, developmental timing and available support can all distinguish histories that receive the same simple event count. An exposure measure and the person's response to it are different variables.

A longitudinal design can measure early adversity exposure, later psychological stress and subsequent symptoms separately. This allows a stress sensitization hypothesis to predict a different relation between later stressors and symptoms according to earlier history. Constance Hammen and collaborators tested that possibility in a prospective study of young women.^[ref]

An observed association does not uniquely identify a biological mechanism or make exposure randomly assigned. Measurement differences, earlier symptoms and confounding remain relevant. Nor does evidence of varied responses justify treating additional adversity as a beneficial intervention.

A clinical psychologist who investigated genetic and environmental contributions to adversity exposure-conditioned adaptation scores.^[ref]

Measurement relating documented adversity to subsequent adaptation. A design specifies adversity exposure, outcome, baseline functioning and follow-up; capacity questionnaires, trajectories and adversity exposure-conditioned regression residual scores operationalize different questions.

A resource associated with more favorable functioning across the adversity exposure levels under study. This describes a general favorable association, distinguished here from an adversity exposure-dependent stress-buffering interaction. Terminology varies across the literature, so a study should specify its statistical and causal meaning.

An adversity exposure-conditioned adaptation measure. With distress $D_i$, adversity exposure $S_i$ and predicted distress $\hat{m}(S_i)$, the displayed convention makes higher scores mean less distress than predicted. The result depends on adversity exposure measurement, reference population and model. A regression residual can include measurement error and omitted causes rather than a distinct protective capacity.

For ordinary least squares $D=X\hat{\beta }+e$, the normal equation gives $X^{T}e=0$. Thus $R=-e$ is also orthogonal to the fitted predictors; with an intercept its sample mean is zero. A zero in-sample linear association between adversity exposure and this score can therefore be an algebraic consequence of its construction, not evidence that adversity exposure has no effect. Independent validation is needed before assigning substantive meaning to the regression residual.

A proposed protective effect of manageable prior challenges on later responses. A curved association between lifetime adversity and current functioning is not sufficient to establish that effect causally or identify a safe beneficial adversity exposure for an individual. Human observational and animal experimental evidence answer different questions.^[ref]

A pattern in which prior adversity increases sensitivity to later psychological stress, such as a lower subsequent psychological stress level accompanying depression. Demonstrating the pattern does not by itself identify its mechanism or exclude differences in adversity exposure measurement and prior liability.^[ref]