Experimental Design
This large-scale randomized experiment was jointly conducted by Peking University’s Institute of Economic Policy Research (IEPR) and the Chinese Center for Disease Control and Prevention (CDC) in China from October 2013 to October 2014.
Two cities – Ningbo (in Zhejiang province) and Chongqing (a provincial-level municipality) – were specifically chosen as the locations for our study. There are three reasons for this choice. First, these two cities have the highest intensity of CDC branches that are “National Demonstration Units” for chronic disease management; such units have adopted a digital management system that tracks and monitors patients with various chronic diseases, making it convenient for us to identify and locate COPD patients. Second, Ningbo and Chongqing are geographically and socioeconomically representative, to the extent that they are located in the eastern (Zhejiang province) and central (Chongqing municipality) regions respectively. Thirdly, these two cities have very similar latitude – around 30 degree north – and thus face very similar influenza seasons from November to March; this implies that we can run the experiment simultaneously across the two cities.
With the permission of the CDC, we accessed the health records of three counties (a mix of rural and urban) in each city from which COPD patients were then drawn using a stratified sampling method. Specifically, within each county, we randomly selected several communities and assigned them groups that received: the influenza vaccine (hereafter, group A), the pneumococcal vaccine (hereafter, group B), both vaccines (hereafter, group C), and no vaccine (hereafter, group D, which is essentially the control group).
Within each community, our target population for the study comprises seniors aged 60 and above who have been identified as COPD patients by the local CDC authorities. To rule out possible confounding health factors, we then excluded individuals who were (i) inoculated with the influenza vaccine (within the past one year) or the pneumococcal vaccine (within the past five years), (ii) experiencing acute COPD, (iii) suffer from respiratory diseases other than COPD, (iv) undertaking hormonal therapy for cancer, (v) suspected or confirmed to be infected with pneumococcal infection.
The experiment was carried out in two stages. The first stage ran from mid-October to mid-November 2013, when we trained local general practitioners to conduct a baseline survey on all the patients in our sample. This survey collected basic demographic and socioeconomic information, physical condition, COPD status, and medical expenditure in the preceding year. Patients in the three treatment groups were then informed to visit the nearby CDC clinics to receive their allocated vaccine injection. All injections were completed in the first two weeks of November.
The second stage comprises four rounds of follow-up surveys – in the first two weeks of January, March, May, and October in 2014 – on all patients in our sample. These surveys were intended to track their COPD condition and medical expenditure across four different seasons.