Inuence of National Essential Public Health Services Policy on Expenditure for Hypertension in China: A Difference-in-Difference Analysis

Background: The prevention and control of hypertension should be an effective way to reduce deaths and it has been a high priority in China. The Chinese government issued the National Essential Public Health Services Package (NEPHSP) in 2009; this initiative provides free public health services to meet the challenges posed by hypertension. It includes health education, regular health checkups, and regular follow-ups provided to patients with hypertension aged ≥ 35. This study explored the inuence of the NEPHSP on outpatient and inpatient expenditure among patients with hypertension. Methods: Data were mined from the 2011–2015 Harmonized China Health and Retirement Longitudinal Study. The dependent variables were the outpatient and inpatient expenditure of patients with hypertension. The independent variable was dened as whether covered by the NEPHSP in 2013 or 2015. Using propensity score matching (PSM) to match the individual characteristics of hypertension in the NEPHSP-covered group and the NEPHSP-uncovered group, Tobit regression models with difference-in-differences (DID) were used to analyze the outcomes. Results: After PSM, of the 1,956 hypertensive participants, 369 had physical exams covered by the NEPHSP in 2013 and 2015. In 2013 and 2015, the outpatient and inpatient expenses of patients with hypertension increased compared with 2011. A DID estimate for the NEPHSP-covered service was associated with a marginal signicant decrease of RMB 319.79 (p = 0.586) and RMB 1072.02 (p = 0.068) in hypertension inpatient expected expenditure in 2013 and 2015, respectively. The DID estimate showed no signicant change among outpatient expected expenditure. Conclusions: The NEPHSP may reduce inpatient expenditure among patients with hypertension. Further strengthening of the NEPHSP may reduce their burden.

Previous studies have indicated that the number of patients with hypertension covered by the NEPHSP is positively associated with hypertension control rates, medication rates, and blood pressure monitoring rates [11,12]. However, no studies have investigated whether higher rates of medication and blood pressure monitoring are associated with higher costs for hypertension treatment. Further, previous studies on the cost of hypertension treatment did not include the effect of the NEPHSP [13][14][15].
In this study, we used nationally representative longitudinal data to analyze 1) the changes and differences in outpatient and inpatient expenses of hypertensive patients before and after the NEPHSP was implemented and 2) the impact of the NEPHSP on outpatient and hospitalization costs of hypertensive patients.

Data and sample
Data were obtained from the China Health and Retirement Longitudinal Study (CHARLS), a nationally representative survey of individuals aged ≥ 45 that is administered every two years since 2011. The data included 17,708 participants distributed across 450 villages in 150 counties [16]. For cross-national comparisons of other international aging surveys, a Harmonized CHARLS was created to coordinate the CHARLS with the Health and Retirement Survey in the United States, for which detailed information is publicly available online [17].
Patients with hypertension were de ned as respondents who self-reported high blood pressure in 2011 and were not covered by the NEPHSP in that year (hereafter, NEPHSP-uncovered). The nal data set included 3,192 hypertensive patients who were not lost to follow-up and had no signi cant variables missing in 2011, 2013, and 2015 ( Figure 1). This study reported the direct spending of outpatients and inpatients separately and used the data as the dependent variable in the models. All outpatient expenditure in the past month was recorded, including both treatment and medication costs. Direct medical costs were included in inpatient expenditures during the past year, while indirect medical costs were excluded. To identify total hospitalization expenditure in the past year, total medical cost of doctor visits, and amount paid by their insurance company, we used the following items from the CHARLS baseline questionnaire: "How many times have you received inpatient care?," "How many times did you visit a medical facility?," "What is your total hospitalization cost?," and "What is your total outpatient cost?" If the respondent had two or more inpatient or outpatient treatments in the past year or month, then the respondent was asked to list the total medical costs for all visits.
The essential independent variable was the NEPHSP-covered participants. To determine whether hypertensive patients were covered by NEPHSP, we used the question "When did you have your last physical examination?" to identify responders who had received physical exams in 2011, 2013, or 2015. The question "Who paid for your last physical examination?" measured whether the medical costs were covered by the NEPHSP, given that the NEPHSP includes a free physical exam at least once a year for patients with hypertension aged ≥ 35.
Respondents who chose "government" were the treatment group, and respondents who chose "non-government" had not received a free medical exam and were de ned as the comparison group.
The covariate variables for this study consisted of individual socioeconomic characteristics and health information, such as age (≥ 65 or not), sex (male or female), marital status (living with or without a partner), occupation (farmer or not), education (1 = Less than lower secondary education, 2 = Elementary school, and 3 = Middle school). Household income classi ed by quartiles into four groups: poor (< RMB 3,335), low income (RMB

Statistical analysis
As indicated above, respondents covered by NEPHSP between 2013 and 2015 were de ned as the treatment group, while the comparison group had not received this service. First, we found a gap in the socioeconomic and health characteristics between the two groups of hypertensive patients. The covariates of the two groups of hypertensive patients in 2011 were matched by propensity score matching (PSM) [18], which enables us to calculate weights based on the socioeconomic characteristics and health information of patients with hypertension that yield unbiased estimates of the impact of factors of interest [19]. We adopted the 1:4 neighbor matching method to match the treatment and comparison groups and retained the matched data for the nal analysis.
Second, based on the matched data, a difference-in-differences (DID) method was used to analyze healthcare expenditure changes from before the NEPHSP (2011) compared to after (2013 and, separately, 2015). DID can effectively detect the intervention effect between the treatment and comparison groups and isolate the time trend unrelated to the intervention [20]. The effect of the NEPHSP is estimated by comparing the differences between two changes in outcomes: (1) changes between pre-and post-NEPHSP within the treatment group and (2) the preand post-intervention periods in the comparison group [21]. Given that the skewed distribution of health cost data (which contain many zero values) violated the normal distribution assumption of the ordinary linear model, a Tobit model is suitable for the analysis [22]. Therefore, a panel data Tobit regression model was employed for continuity outcomes to estimate NEPHSP's effect on each group's healthcare expenditure. More than 50% of the cost of patients with hypertension in our sample has a value of 0, and the values that are not 0 conform to the normal distribution; we reported the mean value when describing the sample. A P-value <0.1 was considered statistically signi cant. All analyses were performed using Stata software, version 16.

Ethical approval
All participants provided written informed consent and ethical approval for collecting data on human subjects was obtained from the appropriate Biomedical Ethics Review Committee.

Sample characteristics
Additional Table 2 presents the socioeconomic and health characteristics (N = 3,192) for each group. Compared with 2011, the proportion of patients with hypertension who were aged ≥ 65, poor-house-income, BMI ≥ 24, and good self-reported health increased in 2015 for both groups, while having a partner, farmers, having insurance, and low middle high-house-income declined in 2015. The sex, marriage, education, and residence status of the patients with hypertension remained constant for both groups. Table 1 illustrates the socioeconomic and health characteristics before and after the PSM in 2011. Before matching, the samples differed signi cantly in terms of age, elementary school education, middle school education, and high income. After matching, the differences in the socioeconomic and health characteristics between the two groups became insigni cant.

Baseline characteristics after PSM
Additional les Figure 1, Figure 2, Figure 3, and Figure 4 illustrate the standardized bias across the covariates in the -10% to 10% range, propensity score distribution, and kernel density across the two groups' propensity scores before and after matching, and the matching effect was satisfactory.

Discussion
Our results revealed that the inpatient expenditure of patients with hypertension decreased after the expanded NEPHSP was implemented in 2015. Previous research indicates that expanded NEPHSP implementation could improve the rate of hypertension control, antihypertensive medication use, and blood pressure monitoring [11]. Other research has indicated that providing free public health services to patients with hypertension can effectively reduce their burden [23]. The NEPHSP may have a positive in uence that is related to improvements in hypertension diagnosis, treatment, and control. Indeed, some signs point to a shift toward reactive care for prevention [24], which may be positively correlated with promoting healthy lifestyle traits, such as a low sodium diet [25], physical activity, weight loss, and smoking and drinking cessation [26]. It may also signal decreases in hospitalization rates, lengths of stay, or procedures for complications [27]. The NEPHSP provides free preventive care services for patients with hypertension to prevent or delay comorbidity and complications of the disease and lower overall healthcare costs. These results are similar to those of a study conducted in Japan that demonstrated that free screening and treatment services for patients with hypertension were associated with a 42-75% reduction in stroke incidence [28]. Thus, it is not surprising that in China, the expanded NEPHSP can reduce the disease burden of patients with hypertension.
There was an overall upward trend in expenditure associated with hypertension from 2011 to 2015, which might be related to the increasing incidence of hypertension in China. China is one of the fastest growing countries all over the world [29], the prevalence of self-reported hypertension among people aged 15 and over rose from 6.7% in 2008 to 14.2% in 2013. Meanwhile, the number of patients with hypertension older than 65 increased from 21.6% to 37% and the number of patients with hypertension aged 45 to 64 also doubled during this period [30].
The life expectancy of patients with hypertension and incidence of young hypertensive patients increased.
Correspondingly, healthcare expenditure increased, as people with hypertension live longer and their chances of developing comorbidities and complications increase [26,31]. One study in China revealed that 87% of heart disease deaths, 71% of stroke deaths, 54% of ischemic heart disease deaths, 41% of other cardiovascular disease deaths, and 43% of chronic kidney disease deaths were attributable to hypertension [32], which may also be one of the reasons for the increased cost for patients with hypertension observed in this study.
We noted that healthcare costs for patients with high blood pressure increased more slowly in the two groups after 2013. This may be related to improved health literacy among patients with hypertension, or it could be due to "spillover effects" from the NEPHSP. The same spillover effects have been observed in other policy studies [33,34].
Our results suggest that there might be a positive spillover effect between the treatment group and the comparison group, but a negative spillover effect between the expenditure of outpatients and inpatients.
After 2013, the outpatient and inpatient expenditure of patients with hypertension who were not covered by the NEPHSP rose slowly. Those covered by the NEPHSP displayed a slow upward tendency in outpatient services and a downward tendency in hospitalization services. These ndings suggest that the implementation of the NEPHSP might be achieving its goals of improving hypertension management. The same results have been con rmed in other studies in China [11,35]. Compared with 2002, the number of patients who were aware they had hypertension increased by 54 million, the number who were treated increased by 53 million, and the number whose blood pressure was under control increased by 0.25 million. This is largely because of the government's continued efforts to reform the healthcare system and equalize public health services.
We acknowledge that there are several limitations to this study. First, although PSM was used to eliminate some individual selection bias factors, there are numerous confounding factors, such as the living environment, social network, access to health care in the place of residence, medical consumer price level, and healthcare supply in the place of residence. Second, our dependent variable fails to isolate the costs purely because of hypertension, and other comorbidities of the patients with hypertension may interfere with the results. Future studies must link the survey data and the medical treatment data to obtain the pure cost of hypertension. Moreover, there was a considerable amount of zero values in the dependent variable, which, despite the use of the Tobit model, may still affect the result estimates, as we cannot determine whether the cost is due to patient visits or non-visits to healthcare providers. Finally, we used data for patients with hypertension aged 45 and over in the CHARLS, but patients with hypertension aged 35 and over were covered by the NEPHSP, which may have in uenced our estimates. In the future, we will use more nationally representative samples and include more variables to study this issue.

Conclusions
In China, the implementation of the NEPHSP may have reduced the healthcare expenditure of patients with hypertension. This may be due to guidance for patients with hypertension to regularly visit their doctor, improve medication and control, or reduce complications and hospitalization. The NEPHSP is an important health policy that encourages patients with hypertension to seek medical care reasonably and regularly. In the future, nancial compensation should be increased, the catalog of free screening services for chronic diseases should be expanded, the occurrence of chronic disease complications should be avoided or delayed, and the burden of chronic diseases should be reduced. For policymakers, the NEPHSP may have begun to achieve its goals of increasing the health awareness of patients with hypertension and reducing their nancial burden.   Figure 1 Flow chart of the participants.

Figure 2
Comparison of outpatient expenditure of the treatment and comparison groups before and after PSM (RMB).

Figure 3
Comparison of inpatient expenditure of treatment and control comparison before and after PSM (RMB).