The Extremadura Health Service includes eight different Health Areas. Health Areas are geographical divisions with a relatively decentralized management of primary care services in each area, as is the case across all Spanish autonomous communities. The eight Health Areas of Extremadura are in turn subdivided into a total of 114 Basic Health Areas. According to the Extremadura Health System, there were a total of 9622 people diagnosed with COPD in Extremadura in April 2015 (79.9% males, 79.3% ≥ 65 years), spread across its eight Health Areas. Therefore, our population was 9622 individuals.
This study uses data from a larger study dedicated to the socio-economic burden of COPD in Extremadura . This was a cross-sectional observational study that used probabilistic sampling stratified by Health Area in order to obtain a representative sample of patients with COPD in Extremadura. In the first stage, a randomized sample representative of the adult population diagnosed with COPD in Extremadura (n = 386, 95% confidence level, 5% sampling error) was calculated based on the prevalence of COPD in the population aged 18 and over in Extremadura. In the second stage, two age group quotas (under 65 years of age and 65 and over) and two gender quotas per age group were established within the sample. These represented the different age and gender prevalence groups in each of the eight Health Areas of Extremadura. We then randomly selected 18 Basic Health Areas distributed across the eight Health Areas of Extremadura, proportionately to the number of Basic Health Areas in each Health Area. The number of patients and age/gender quotas to enrol in each Basic Health Zone were assigned in such a way that the theoretical sample was proportionally distributed across Health Areas. Likewise, within each Health Area, the quotas were proportionally distributed across age and gender of the population with COPD residing in each of the Health Areas.
The present study included people diagnosed with COPD according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) classification criteria  at least 12 months before their inclusion in the study, 18 years of age or older, residents of Extremadura whose primary care electronic medical records were available for the 12 months prior to the collection of the data, who provided informed consent to participate in the study in accordance with local regulations. Patients with any limitation that, according to the researchers’ best judgement, could affect the reliability of their answers were excluded (e.g., patients without knowledge of Spanish, or patients with any evident cognitive impairment). Patients who had participated in any clinical trial in the 12 months prior to the collection of data and pregnant women were also excluded.
A total of 18 previously trained researchers participated in the data collection process, one in each of the 18 Basic Health Areas selected. Researchers received a randomly ordered list of all the patients diagnosed with COPD who resided in their corresponding Basic Health Zone. The patients’ name, contact telephone number, and address were included in the list as they appeared on their clinical record. This information was disclosed to field researchers but was never available to the signing authors of this manuscript. Researchers contacted patients over the telephone following the order in their list. Whenever a patient was not available on the telephone, researchers contacted the next patient on the list. Once telephone contact was established, researchers verified with the patient that inclusion/exclusion criteria were met and, if so, asked the patient to meet in person either in the patient’s home or in their primary care centre, whichever was preferred by the patient. Patients were recruited this way until all age and gender quotas were completed for each Basic Health Zone. The reasons reported by researchers for not enrolling a patient included: the patient does not feel comfortable talking to a doctor, the patient feels nervous and apprehensive about the study, the patient will not be available for a while (e.g. holidays), the patient did not consent to participate, the patient was not reachable after several calls, the patient had a cognitive deficit (Alzheimer’s disease), the patient has moved to another autonomous community or to another Basic Health Area, there was no contact information on the clinical record, and the patient did not recognize having any respiratory disease.
The fieldwork was carried out from July 10th to November 11th, 2015, and included one single visit per patient. Besides collecting information related to healthcare and non-healthcare resource utilization (results published elsewhere ), information was collected on patients’ quality of life at the time of the visit using the EQ-5D-5L questionnaire (general quality of life) and the SGRQ-C questionnaire (quality of life of patients with airway obstruction). Information on comorbidities was collected directly from the patients’ electronic clinical records. Prior to data collection, patients were informed about the study objectives and data confidentiality. Patients provided their written informed consent to participate in the study and to release information, according to the Spanish legislation. Permission to perform the study was obtained from the Clinical Research Ethics Committee of the University Hospital Infanta Cristina (Badajoz).
Health-related quality of life
Two validated questionnaires were used to assess the HRQL of the patients. The first questionnaire was the EQ-5D-5L, which was used to measure general HRQL at the time of the visit, as reported by the patient. This questionnaire gathers information relative to five health-related dimensions (mobility, self-care, daily activities, pain or discomfort, and anxiety or depression), and each dimension has five response options depending on the intensity level of the problem (no problems, slight problems, moderate problems, severe problems, and extreme problems). Thus, the EQ-5D-5L allows for the collection of a total of 3125 possible health states. Each state is assigned a utility value based on the rates validated for Spain , which ranges from 0 (equivalent to death) to 1 (perfect health status). Values below zero are possible and are understood as a health status that is worse than death. This questionnaire further provides a visual analogue scale (VAS) where the patient self-evaluates their health. The VAS ranges from 0 (worst imaginable state) to 100 (best imaginable state) .
The second questionnaire was the SGRQ-C, which quantifies the impact of COPD and/or asthma on health and well-being, as perceived by the patients. The questionnaire consists of 50 items divided into three component scores: Symptoms, Activity and Impacts. The Symptoms score refers to the frequency and severity of respiratory symptoms, the Activity score is indicative of dyspnoea-related activity limitations, and the Impacts score shows the psychological and social changes produced by the disease. The items are formulated in two different manners. The first method involves five response options, allowing only a single option to be marked. The second method involves a dichotomous answer: yes/no. A Total score is calculated taking into account all three component scores. All scores range between 0 (without any impact on the quality of life) and 100 (maximum impact on the quality of life) . Researchers provided patients with an electronic tablet containing both questionnaires to be self-administered by the patients.
Level of severity
The level of severity according to the GOLD scale (levels I to IV, where I corresponds to mild airflow limitation and IV corresponds to very severe airflow limitation, in patients with FEV1/FVC < 0.70)  was not available in the primary care clinical records of a large number of patients. As we had no access to clinical records from pulmonology services (these generally include the GOLD classification), we used three complementary sources of information for the elaboration of a single severity variable. Accordingly, the following steps were taken to determine COPD severity: first, the GOLD classification of the patient was used if it was included in the clinical records (10.6% of the patients). Second, in the absence of a GOLD classification, the GOLD classification was calculated from the FEV1% predicted values as long as these data were indicated in the clinical records (30.3% of the patients). This calculation was done following the GOLD classification of airflow limitation severity criteria . Third, in cases where no GOLD classification or FEV1% data were available, we used the description made by the doctor in the patient’s medical records (0.8% of the patients). Finally, if all the previous data were not available, an “unknown/not available” severity level was assigned. In our sample (n = 386), 58.3% of patients (226 patients) lacked information on severity level.
Descriptive statistics (number of valid cases, mean, and standard deviation) were calculated for continuous variables, and frequencies and percentages were calculated for categorical variables. An analysis was performed using the total sample, and comparisons were made based on the level of severity, gender, and age group. For the analysis according to severity, GOLD I and II categories were grouped together, and GOLD III and IV categories were grouped together with the aim of optimizing the statistical comparison. For the comparison of a quantitative variable with a qualitative variable, nonparametric techniques were used (Mann-Whitney U and Kruskal-Wallis U tests). For the comparison of two qualitative variables, the Chi-square test was used. To analyse the explanatory factors of HRQL (utility and SGRQ-C total score), a stepwise multiple regression was used. The regression variables were gender, age in years, education level (no education and primary education vs. secondary and university education), COPD severity level (GOLD I-II vs. GOLD III-IV), number of exacerbations in the last 12 months, and number of comorbidities (this variable includes all comorbidities reported in the patient’s clinical record that were current at the time of the interview). Values of F ≤ 0.05 and F > 0.10 were established as input and output criteria for the explanatory variables, respectively. This process was repeated until the model did not improve. Finally, to correlate the scores of the questionnaires, Spearman’s rho correlation coefficient was used. For all analyses, the limit of statistical significance was p < 0.05. The data were analysed with the statistical package IBM SPSS Statistics V22.0.