This study indicates that in COPD patients in primary care, psychological factors contribute to HRQoL. More positive perceptions about COPD and lower levels of depressive symptoms were associated with better HRQoL. Significant relations between psychological factors and DA (measured by FPI) were not found.
To appreciate the findings of this study, some limitations need to be considered. First, the cross-sectional nature of our study prohibits conclusions on causal relationships. Longitudinal data will facilitate the explanation of the relationships among psychological determinants, DA, and HRQoL in more detail. Second, the βs in the regression models were small, indicating small clinical changes per unit change.
Third, although our sample size was adequate given the research question, it did not allow us to conduct subgroup analyses per GOLD grade. Therefore, we could not describe the associations in the different stages of COPD.
The strength of the present study is its generalizability. In our study population, 60% of the patients had GOLD grade II, indicating mild to moderate COPD, which is in line with the population of COPD patients in primary care . Moreover, we did not exclude patients with co-morbidities. Therefore, our study population is representative of the primary care population.
The multivariate approach (i.e., including the combination of different types of psychological factors) to explain the complexity of living with COPD represents another strength of this study.
The findings of our study are in accordance with results from previous studies concerning illness perceptions in COPD patients. Scharloo et al.  demonstrated that COPD patients with more positive beliefs about the effect and outcomes of their illness and with fewer strong emotional reactions to the illness had higher HRQoL scores. In a study by Fischer et al. , COPD patients’ beliefs about the effectiveness of medical (pharmacological) treatment in COPD were shown to be related to better outcomes in COPD.
Whereas in other patient groups, such as patients with diabetes, proactive coping has been related to better outcomes in health behavior [27, 33], we could not confirm the hypothesis that COPD patients with proactive competencies have better DA and HRQoL. Possible explanations may include our relatively small sample and the mild COPD population we studied. It is unknown what this association is for COPD patients with GOLD grade III and IV, who have more potential threats to their health.
In this study, 22.2% of the patients had depressive symptoms, which is comparable to the prevalence of depressive symptoms (24.6%) in a meta-analysis study by Zhang . However, contrary to other studies [39, 40], daily activities were not associated with depressive symptoms in our study. This finding may partially be explained by the use of other DA and dyspnea measurement tools. Nevertheless, in line with other studies [13, 41], depressive symptoms were associated with HRQoL.
The finding of our study that dyspnea contributes to HRQoL is comparable to other studies regarding the association between dyspnea and HRQoL [41–43]. Moreover, our study revealed that 60% of the variance in HRQoL was explained by the combination of illness perceptions, depressive symptoms, and dyspnea.
Although the level of daily activities of COPD patients in this study (1.80) was in line with levels of activity in other studies using the FPI in COPD patients (2.2 in a study by Kapella  and 1.87 in study by Wall ), in contrast to our hypothesis, we did not find associations between psychological factors and DA. This finding is in contrast to the results from previous studies concerning relationships between psychological factors and DA [45–47]. This finding could be explained by the use of different measurement tools for DA. Fischer et al.  used walking test results as the outcome parameter, in contrast to our study, which used the FPI questionnaire. A possible explanation is that a walking test measures the physical capacity or ability to participate in day-to-day activities [48, 49], whereas the functional performance inventory measures self-reported activities in daily life .
In other studies concerning factors affecting health status [40, 45], other DA measurement tools (Saint George’s Respiratory Questionnaire and the Pulmonary Functional Status Tool) were used. Obviously, other factors are likely to influence the activities people choose to perform on a daily basis, such as environmental factors, medical history, and other personal characteristics . In our study, dyspnea was significantly associated with DA, which is in line with results from other studies [50, 51].