2. Insurance Coverage, Provider Contact, and Take-Up of the HPV Vaccine
2.4. Results
2.4.2. Potential Mechanisms: Health Insurance Coverage
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a Tdap booster for school attendance, because states with these policies have higher vaccination rates (Carpenter and Lawler 2019) and, consequently, smaller margins for adjustment. I show that while the point estimate for teens residing in states with Tdap school requirements is negative and statistically insignificant (column 4), Medicaid expansion was associated with a 3.3 percentage point increase in Tdap vaccination for teens in states without Tdap school requirements (column 5). Similarly, I find suggestive evidence that Medicaid expansion was associated with an increase in meningococcal vaccination (column 6). Consistent with the estimates for the Tdap booster, the relationship is driven by a 1.7 percentage point increase in vaccination for teens residing in states that did not require students to obtain the meningococcal vaccine (column 8).
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In Table A9, I show that the increases in health insurance coverage were entirely attributable to changes in the probability that teens had public health insurance (Panel I). I do not find any evidence that Medicaid expansion significantly crowded out other forms of health insurance (Panel II). Beginning in 2016, health insurance information is only available for teens with adequate provider data, while in prior years it is available for all teens.12 In order to leverage as large of a sample as possible, I use all observations with data on health insurance coverage.
However, I show in Table A10 that the estimated increase in insurance coverage is actually larger if I restrict my sample to the 2010-2015 period prior to the change in availability.
The estimated relationship between the ACA Medicaid expansion and HPV vaccination is larger than the relationship between expansion and health insurance coverage (3 percentage points vs. 1-2 percentage points). There are several possibilities to explain this pattern. One explanation is simply that the relationship between Medicaid expansion and insurance coverage is more tightly estimated. For health insurance coverage, the 95 percent confidence interval indicates that Medicaid expansion was associated with a 0.3-2.3 percentage point increase in the probability that a teen had health insurance and a 0.3-6.3 percentage point increase in the probability of HPV vaccine initiation. As such, there is considerable overlap in the estimates.
I also estimate smaller increases in insurance coverage than other papers examining
“welcome mat” effects. Studying expansions in parental Medicaid eligibility between 1996 and 2007, Hamersma, Kim, and Timpe (2018) found a 3 (5) percentage point increase in the probability
12 Prior to 2016, the NIS-Teen provided a series of variables regarding the teen’s health insurance coverage.
Specifically, it asked whether the teen was covered by (i) employer-sponsored insurance, (i) Medicaid, (iii) S-CHIP, (iv) Medicaid or S-CHIP, (v) Indian Health Service, military health care, Tricare, CHAMPUS, or CHAMP-VA, or (vi) any other health insurance. All of these variables are indicators, and the public insurance questions varied by the teen’s state of residence. Since 2016, the NIS-Teen has constructed a single insurance status variable taking on values 1-4 which harmonizes the underlying data. I define a teen as on public health insurance of s/he is covered by Medicaid or S-CHIP from 2010-2015 and if s/he is covered by Medicaid from 2016-2018. I show in Table A10 that my estimates are robust to only using the 2010-2015 period.
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that a child had any (public) health insurance (Tables 3 columns 1 and 2). Similarly, Aizer and Grogger (2003) found that expanded parental eligibility for Medicaid increased the probability that children had health insurance by 4 percentage points. Leveraging variation from the fact that some California counties opted to expand Medicaid in 2011 under the ACA, Sommers et al. (2016) found that children residing in these counties were 3.2 percentage points more likely to have public health insurance.
Yet even a 3-5 percentage point increase in insurance coverage would likely be too small to completely explain the increased vaccine take-up. An alternative explanation is that Medicaid expansion made parents more likely to interact with the health care system, which gave them more chances to learn about the HPV vaccine. When examining state Medicaid eligibility changes from 1996-2002, Busch and Duchovny (2005) found that increased eligibility resulted in approximately 30 percent of women being screened for breast cancer and cervical cancer that otherwise would not have been screened. Similarly, Simon, Soni, and Cawley (2017) found evidence that the ACA Medicaid expansion increased the probability that some women received cervical cancer screenings. By increasing the probability that women received cervical cancer screenings, the Medicaid expansion may have provided mothers with a new opportunity to learn about HPV vaccination.
In order to gauge the plausibility of these spillovers, it is important to consider how the ACA Medicaid expansion affected the insurance coverage of these teens’ parents. Frean, Gruber, and Sommers (2017) found that new Medicaid eligibility reduced the likelihood that an adult was uninsured by 8.9-13.7 percentage points with larger effects (10.7-19.7 percentage points) for those who gained coverage through the early ACA expansions. The authors also found a 2.6-4.6 percentage point increase in the probability that already-eligible adults became insured. The
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authors found no evidence of crowd-out. These large coverage gains suggest a sizable increase in the probability that these teens’ parents interacted with the health care system.
Another possibility is that Medicaid expansion affected teens’ utilization of health care services. There are a number of papers documenting a positive association between parents’ health care utilization and children’s use of services (Hanson 1998; Goedken, Urmie, and Polgreen 2014), as well as a positive association between parents’ insurance status and children’s health care utilization (Davidoff et al. 2003; Dubay and Kenney 2003; Gifford, Weech-Maldonado, and Short 2005). However, I am unaware of any published paper employing a research design intended to uncover a plausibly-causal relationship. As such, a further contribution of my current study is to provide evidence that Medicaid expansion was associated with changes in children’s health behaviors which cannot be fully explained by increased insurance coverage.