In this study, we found that patients self-reporting at least daily weight monitoring adherence did not have reduced rates of HF hospitalization compared to those self-reporting less frequent weighing adherence at 12 months. In contrast, we found that patients with ≥80% diary-recorded weight monitoring adherence had a statistically significantly lower rate of HF hospitalization than those with <80% adherence over 12 months of follow-up. Our findings suggest that diary-recorded measures of adherence may accurately identify optimal self-care that is associated with a reduced risk of HF-related hospitalizations.
HF self-care behaviors are frequently assessed through global self-reported measures, including the Self-Care of HF Index (SCHFI),  the revised Heart Failure Self-Care Behavioral Scale [15, 16], the European HF Self-Care Behavioral Scale (EHFScB Scale),  and the Revised HF Compliance scale, [5, 17] all of which contain an item to assess weighing behavior. Better HF care/behavior scores on respective indices/scales have been associated with improved clinical outcomes [17, 18]. In studies that have specifically evaluated the association between weight monitoring adherence and clinical outcomes, the association between adherence and clinical outcomes has been variable based on the adherence measure used [17, 19, 20].
Daily weight monitoring is a mainstay of HF self-care, yet the most clinically meaningful measure to evaluate adherence to this behavior is not clear. Comparisons have been made between measures that are self-reported and measures obtained from repeated sampling of current behaviors or symptoms over a time period, termed “ecological momentary assessment” (EMA), in the work of Shiffman and colleagues . EMA measures have the potential to “minimize recall bias, maximize ecological validity, and allow study of microprocesses that influence behavior in real-world contexts” (pg 1) . EMA can be collected many ways, including diaries, telephone calls, and electronic records. The main objective of EMA is to ascertain multiple samples of symptoms or behaviors experienced at the time the sample is collected. Self-reported and EMA measures have been found to be discrepant in studies from various populations, including patients with alcoholism,  tobacco use,  urinary incontinence,  and headaches .
Discrepancies between self-reported and EMA measures of medication adherence [e.g., medication event monitoring systems (MEMS) caps (medication bottle caps that record times/dates that bottles are opened)], have also been noted in patients with HF [19, 20]. Such discrepancies between adherence measures can be attributed to a number of characteristics, such as the frequency with which measures are collected, the duration of time over which measures estimate behavior, the types of behaviors being evaluated, and other factors . Overall, self-reported measures are at risk for systematic recall bias when compared to EMA measures .
In our study, measures used to assess daily weight monitoring adherence fall into the general categories of self-reported recall and EMA from a daily diary. We found that a self-reported recall of optimal adherence at 12 months was associated with a somewhat higher risk of HF-related hospitalizations that was not statistically significant; the small size of the group self-reporting optimal adherence likely contributed to less precision in this outcome. Yet, we did find an association between diary-recorded weight monitoring adherence and HF-related hospitalizations at multiple thresholds of adherence, with an effect size that strengthened with increasing thresholds. Adherence thresholds ranging down to ≥60% of days were associated with decreased risk for HF-related hospitalization, suggesting benefit even at thresholds lower than our pre-specified cut-point of ≥80%.
One may speculate whether completion of weight diaries in this study is merely a reflection of program engagement and/or more advanced HF self-care skills/knowledge. To evaluate whether program engagement may have explained some of this association, we added the number of educator calls into our adjusted model and found that this did not lead to attenuation of the IRRs from our main analyses (results not shown). We theorize this is because the number of educator calls may have varied based on a range of factors including: a patient’s engagement in the program, lack of mastery of educational material that required more calls, or even patient-initiated calls due to concerns about their regimen or symptoms. Of note, the weight diaries in this study were used to teach a majority of patients (72% of intervention arm patients) how to self-adjust their diuretics based on weight. Although the observed association could have been partly related to this aspect of the intervention, the proportion of patients who were taught diuretic self-adjustment did not differ significantly by adherence in either self-reported or diary-recorded groups (Table 1).
With regard to study limitations, our self-reported adherence question did not specify the duration of time for which patients were to report weighing behavior, which likely increased recall bias in responses. In addition, given that 85% of patients self-reported weighing at least daily at 12 months, patient responses to this question may not have accurately reflected behavior, potentially due to social desirability or other factors. It is important to note that the surveys were delivered by masked outcome assessors. The smaller sample size and very low rate of HF-related hospitalization in the group that self-reported sub-optimal adherence contributed to less precision in our results and lack of statistically significant findings.
In addition, our measure of diary-recorded weight monitoring averaged adherence over the entire follow-up period. As such, it is possible that adherence directly preceding HF hospitalizations differed from overall adherence; however, in a prior case–control study nested in this same study population, we found that diary-recorded weight monitoring adherence (≥80%) in the week preceding HF emergency department visits or hospitalizations was similarly protective .
Our comparison between self-reported and diary-recorded adherence measures was not a direct comparison between randomized groups of individuals, but instead a comparison of how different measures of adherence were associated with clinical outcomes in the same group of individuals. We noted baseline differences between groups who were optimally adherent and sub-optimally adherent to both self-reported and diary-recorded measures; thus selection bias or unmeasured confounding may have affected our results. However, we attempted to mitigate such differences by adjusting for these variables in our analysis; in addition, we found comparable results to our main analysis when we performed a sensitivity analysis in which we included patients who never submitted a weight diary. The generalizability of our findings may be limited by our younger patients with less advanced HF than in other studies of HF self-care [1, 26]. Strengths of this study include a diverse, well-characterized sample drawn from a multi-site trial and rigorous outcome assessment.