This study provides evidence of the reliability and validity of the IVRS-administered abbreviated 9-item TSQM without the side effects domain (TSQM-9). There was evidence of construct validity based on structural equation modeling findings of the observed data fitting the Decisional Balance Model of Treatment Satisfaction even without the side effects domain. TSQM-9 domains had high internal consistency as evident from Cronbach's alpha values of 0.84 and over. TSQM-9 domains also demonstrated good test-retest reliability, with high intraclass correlation coefficients exceeding 0.70. As expected, the TSQM-9 domains were able to differentiate between individuals who were medium and low compliers with a moderate effect size. There was also evidence of convergent validity, with significant correlations with the medication adherence scale.
The TSQM-9 was developed due to the need for using a measure of treatment satisfaction that was designated to minimize interference in routine clinical care in the context of naturalistic study designs. The side effect domain of the TSQM Version 1.4 queries the patient about their experience in relation to side effects and has a potential to provoke the physician to assess the presence or absence of adverse events in a way that is clinically atypical, affecting the naturalistic design of a study . It should be noted that we do not recommend the use of TSQM-9 over the earlier versions of the TSQM in clinical studies where there is no such possibility of the side effects domains interfering with study objectives and where the outcome of investigational drugs are being studied. Clearly, based on the conceptual framework of TS-M, patient's perception of side effects with their medication is an important component of satisfaction with their medication. However, there are specialized studies in which the side effects domain has potential to interfere with objectives of the study; the TSQM-9 is intended to provide a validated instrument for such scenarios.
It is important to note that although the side effects domain was not included in TSQM-9, any unpleasant experiences with a medication are likely to be captured in the TSQM global satisfaction items. As a result, even without the side effects items, the TSQM-9 allows for patients to weigh the pros and cons of medication and the less favorable aspects of patients' experiences with their medications would be captured.
In this study, we found that the convenience domain had strongest association with medication adherence followed by effectiveness and global satisfaction. In previous TSQM validation analysis, global satisfaction had the strongest association with medication adherence . This association may be reflective of the hypertensive patient population. In an asymptomatic chronic condition like hypertension, the convenience domain becomes an important factor for medication adherence given that the patient has to take their medications daily without any apparent symptomatic changes in their condition.
One of the limitations of this study was that it was conducted in a homogenous sample of patients using hypertensive medications. Since the TSQM is a generic measure of patients' satisfaction with their medication, validation in a more heterogeneous representative sample, containing, for example, patients with different chronic medical conditions would have improved the robustness of results. Future studies on the performance of the TSQM-9 in other patient populations are recommended. In this study, differences were observed on demographic characteristic between responders to the study invitation and non-responders. Further, there were some differences on race/ethnicity between study completers and non-completers. However, given that the purpose of this study was instrument validation and that the study subjects used in the analysis had a good gender and racial/ethnic mix, these differences are unlikely to bias the study results.
Another potential limitation of this study is the use of a 7-item modified Morisky scale for the validation of TSQM-9. An item from the original Morisky scale related to stopping medication because of feeling worse with the medication was dropped due to similar concerns about the item interfering with the treatment process in a naturalistic study design . However, as discussed earlier, deleting this item resulted in minimal change in the internal consistency of scale as well as the sensitivity and specificity of the scale for identifying lower vs. higher adherers.
Despite these limitations, the TSQM-9 may prove to be a useful measure to assess treatment satisfaction with medication in patients with hypertension when real-world outcomes are of interest and there is a need to minimize interference to the behaviors of health care providers and patients alike.