Letter to the Editor: What Kind of Support Do SMA Families Need?-Reflections Based on Caregiving Roles.

Intensive longitudinal study designs, including ecological momentary assessments (EMA), experience sampling method (ESM) and daily diary methods, have been increasingly applied to measure short-term changes in posttraumatic stress disorder (PTSD) symptoms (e.g., ; ). Such designs are very useful for PTSD research, given their potential to minimize recall bias, to capture rapid symptom fluctuations, and to examine momentary and temporal associations between symptoms (; ). Another key advantage of these designs is their ability to monitor within-person symptom variability across time (). Specifically, they allow researchers to measure intraindividual means (iM) and variability (IIV), which represent a person’s average symptom level and within-person symptom fluctuations across assessments, respectively (). Such data provide valuable information about how individuals differ from one another on PTSD symptom changes across time and how PTSD symptoms change within individuals over time, which can potentially inform personalized interventions and clinical decision-making. Indeed, studies using EMA, ESM, or daily diary methods to examine PTSD symptom changes over short time periods or in response to contextual factors (e.g., ; ) have demonstrated utility in helping to better understand the implications of daily PTSD variability for clinical practice. Monitoring fluctuations in PTSD symptoms may enable clinicians to detect early signs of symptom deterioration, refine intervention targets, and deliver more personalized treatments for trauma survivors. For example, found that real-time monitoring of PTSD symptoms and alcohol use in combat veterans can help identify high-risk periods, suggesting opportunities for timely interventions that reduce avoidance-based coping and strengthen self-efficacy. Preliminary evidence also suggests that frequent assessments of PTSD symptoms itself can contribute to symptom reduction. For instance, found that a 2-week EMA protocol assessing trauma-related intrusive memories led to significant reductions in PTSD’s intrusion severity among trauma-exposed adults. Despite growing interest in within-person variability of PTSD symptoms, there remains little to no consensus on the conditions necessary to obtain reliable estimates of PTSD symptom IIV. This measurement property is referred to as within-person reliability, which reflects the extent to which a measure can consistently capture true fluctuations of symptoms within the same individual over time (). In contrast, between-person reliability suggests how consistently a measure distinguishes differences in average symptom levels amongst individuals. Reliably estimating PTSD symptom IIV is particularly important in clinical settings, as it can provide critical insights into symptom dynamics and may serve as key indicator for treatment progress, risk assessments, and treatment adjustments (; ). Further, reliably estimating PTSD symptom iM can more accurately identify high-risk individuals requiring more intensive care or early intervention (). Despite the plethora of psychometric work in the extant literature verifying the between-person reliability of PTSD measures (), there is limited work on within-person reliability of PTSD measures. Notably, existing study findings may be biased if PTSD measures lack sufficient reliability to accurately reflect true symptom fluctuations. To our knowledge, only one study has examined the within-person reliability of an abbreviated 8-item version of the PTSD Checklist for DSM-5 (PCL-5) that was administered over 7 consecutive days (). The authors reported moderate within-person reliability ( = .78) and excellent between-person reliability ( = .99), but this remains one of the few to assess the ability of PTSD measures to capture IIV. Thus, more research is needed to establish reliable methods for measuring PTSD symptom IIV.