Joiner also acknowledges the importance of vulnerability factors as a source of depression chronicity and speculates how self-propagatory processes might interact with vulnerability factors, such as rumination. .
While Joiner's focus on interpersonal factors is a welcome expansion of the variables usually considered, our appraisal is that his article is more of an introduction to these factors, rather than a reasoned argument for their role as mechanisms of depression chronicity. We have organized our comments around three issues: (1) the need for criteria by which to identify causal risk factors, (2) the necessity to further elaborate the mechanisms underlying self-propagatory processes, and (3) the utility of considering separately processes involved in episode onset and episode maintenance. .
RISK FACTOR OR CORRELATE "HOW DO WE KNOW?.
Joiner sets out to identify factors that "explain aspects of depression chronicity" and states that the processes he outlines "serve to prolong or exacerbate existing symptoms or induce the recurrence of past symptoms." As we understand these and similar statements, Joiner seeks to identify causal risk factors for depression chronicity. Such a goal is laudable, but likely to yield ambiguous results without recognition of the conceptual and evidentiary requirements that risk factors must meet. An awareness of these criteria is absent from Joiner's discussion. In our own work, we have found the framework suggested by Kraemer et al. (1997) to be a valuable template for just this type of task. Kraemer and colleagues offer four scientific criteria that must be met in order for any proposed mechanism to be identified as a causal risk factor for any disorder: (1) the factor must be associated with the outcome, (2) the factor must precede the outcome, (3) the factor can change or be changed, and (4) manipulation of the factor changes the outcome. .
Without knowing the extent to which interpersonal behaviors meet, at least, the characterizations described in points 1 and 2, it may be better to view these factors as simply correlated with chronicity, rather than causally implicated in it.
