Table 3.
Detailed explanation of variables included in the DID model
| Variable | Type | Included as | Remark or justification |
|---|---|---|---|
| Admissions/person/year | Continuous | Dependent variable | Newborn admissions were excluded to avoid duplication with delivery admissions |
| HI-PCP | Binary | Independent variable | HI-PCP was an interaction between insurance and time variables. It reflected the policy effect independent of the time trend had the policy not occurred. It was coded 1 if a patient was stateless and was admitted to hospital during 2011–2012. It was coded 0 if the admission was made by a non-stateless patient (either a UCS or an uninsured patient) at any time or by a stateless patient in 2009. |
| Insurance | Indicator | Covariate | Insurance variable was added to capture difference in baseline characteristics of beneficiaries between insurance schemes. |
| Time | Binary | Covariate | Time variable was included to capture effect of natural time trend in the absence of the policy. |
| Age group | Indicator | Covariate | Age group was used instead of age in years because the age distribution was not quite positively skewed (the mean of age was much lower than its median). Thus, using age group instead of age in years fitted the model better and rendered a more sensible interpretation of the results. |
| Disease condition | Binary | Covariate | DRGs were used as an indicator of disease severity of an admission in a given fiscal year. The DRGs contained five digits with the fifth digit indicating disease severity. The fifth digit of 1 referred to mild morbidity, whereas 2, 3, and 4 meant moderate, severe, and very severe, respectively. For any admission in a given fiscal year, a patient given a DRG with the fifth digit of 2 or above was coded as 1 (ever had catastrophic illness). |
| Proximity | Binary | Covariate | A patient with an address in the same district of the hospital was coded as 1 (proximity). This variable was added into the model to mitigate bias from lacking data of patients who did not attend the hospital because of the change in domicile or opting to visit another hospital. |
Abbreviations: DID, difference-in-difference; DRG, diagnostic-related group; HI-PCP, Health Insurance for People with Citizenship Problems; UCS, Universal Coverage Scheme.