Propensity score and difference-in-difference methods: a study of second-generation antidepressant use in patients with bipolar disorder

Clinical and cost outcomes following genomics-informed treatment for advanced cancers

BACKGROUND

Single-arm trials are common in precision oncology. Owing to the lack of randomized counterfactual, resultant data are not amenable to comparative outcomes analyses. Difference-in-difference (DID) methods present an opportunity to generate causal estimates of time-varying treatment outcomes. Using DID, our study estimates within-cohort effects of genomics-informed treatment versus standard care on clinical and cost outcomes.

METHODS

We focus on adults with advanced cancers enrolled in the single-arm BC Cancer Personalized OncoGenomics program between 2012 and 2017. All individuals had a minimum of 1-year follow up. Logistic regression explored baseline differences across patients who received a genomics-informed treatment versus a standard care treatment after genomic sequencing. DID estimated the incremental effects of genomics-informed treatment on time to treatment discontinuation (TTD), time to next treatment (TTNT), and costs. TTD and TTNT correlate with improved response and survival.

RESULTS

Our study cohort included 346 patients, of whom 140 (40%) received genomics-informed treatment after sequencing and 206 (60%) received standard care treatment. No significant differences in baseline characteristics were detected across treatment groups. DID estimated that the incremental effect of genomics-informed versus standard care treatment was 102 days (95% CI: 35, 167) on TTD, 91 days (95% CI: -9, 175) on TTNT, and CAD$91,098 (95% CI: $46,848, $176,598) on costs. Effects were most pronounced in gastrointestinal cancer patients.

CONCLUSIONS

Genomics-informed treatment had a statistically significant effect on TTD compared to standard care treatment, but at increased treatment costs. Within-cohort evidence generated through this single-arm study informs the early-stage comparative effectiveness of precision oncology.

Effect of integrated urban and rural residents medical insurance on the utilisation of medical services by residents in China: a propensity score matching with difference-in-differences regression approach

OBJECTIVES

In this study, we aim to evaluate the effect of urban and rural resident medical insurance scheme (URRMI) on the utilisation of medical services by urban and rural residents in the four pilot provinces.

SETTING AND PARTICIPANTS

The sample used in this study is 13 305 individuals, including 2620 in the treatment group and 10 685 in the control group, from the 2011 and 2015 surveys of China Health and Retirement Longitudinal Study.

OUTCOME MEASURES

Propensity score matching and difference-in-differences regression approach (PSM-DID) is used in the study. First, we match the baseline data by using kernel matching. Then, the average treatment effect of the four outcome variables are analysed by using the DID model. Finally, the robustness of the PSM-DID estimation is tested by simple model and radius matching.

RESULTS

Kernel matching have improved the overall balance after matching. The URRMI policy has significantly reduced the need-but-not outpatient care and significantly increased outpatient care cost and inpatient care cost for rural residents, with DID value of -0.271, 0.090 and 0.256, respectively. After robustness test, the DID competing results of four outcome variables are consistent.

CONCLUSIONS

URRMI has a limited effect on the utilisation of medical and health services by all residents, but the effect on rural residents is obvious. The government should establish a unified or income-matching payment standard to prevent, control the use of medical insurance funds and increase its efforts to implement URRMI integration in more regions to improve overall fundraising levels.

Causal Difference-in-Differences Estimation for Evaluating the Impact of Semi-Continuous Medical Home Scores on Health Care for Children

Difference-in-differences (DID) is a popular approach in observational and quasi-experimental studies to estimate the effects of a treatment with discrete statuses. In many studies, however, the treatment can have a range of dosages or exposure levels. In our paper, "medical homeness" is a semi-continuous score ranging from 0 to 100 to indicate the extent to which a patient-centered medical home model is achieved. We developed a causal DID approach to estimating the effects of a treatment with semi-continuous dosages. The proposed approach allows for mixed-type designs as well as different propensity models. We applied the proposed approach to evaluate the dosage effect of medical homeness scores on the utilization and quality of children's health care. We found that there was a roughly linear effect of medical homeness scores on the annual number of visits to doctor offices when medical homeness scores were below 60 points. The number of office visits did not further increase when medical homeness scores were above 60. A similar relationship was found between medical homeness scores and ratings for health care quality.

Evaluating the Impact of Parent-Reported Medical Home Status on Children's Health Care Utilization, Expenditures, and Quality: A Difference-in-Differences Analysis with Causal Inference Methods

OBJECTIVE

To evaluate the effects of the parent-reported medical home status on health care utilization, expenditures, and quality for children.

DATA SOURCES

Medical Expenditure Panel Survey (MEPS) during 2004-2012, including a total of 9,153 children who were followed up for 2 years in the survey.

STUDY DESIGN

We took a causal difference-in-differences approach using inverse probability weighting and doubly robust estimators to study how changes in medical home status over a 2-year period affected children's health care outcomes. Our analysis adjusted for children's sociodemographic, health, and insurance statuses. We conducted sensitivity analyses using alternative statistical methods, different approaches to outliers and missing data, and accounting for possible common-method biases.

PRINCIPAL FINDINGS

Compared with children whose parents reported having medical homes in both years 1 and 2, those who had medical homes in year 1 but lost them in year 2 had significantly lower parent-reported ratings of health care quality and higher utilization of emergency care. Compared with children whose parents reported having no medical homes in both years, those who did not have medical homes in year 1 but gained them in year 2 had significantly higher ratings of health care quality, but no significant differences in health care expenditures and utilization.

CONCLUSIONS

Having a medical home may help improve health care quality for children; losing a medical home may lead to higher utilization of emergency care.

The impact of influenza vaccination requirements for hospital personnel in California: knowledge, attitudes, and vaccine uptake

BACKGROUND

Seasonal influenza infections are a leading cause of illness, death, and lost productivity. Vaccinating health care personnel (HCP) can reduce transmission of influenza virus to patients and reduce influenza-related absenteeism, enabling the health care system to meet elevated demand for care during influenza outbreaks.

OBJECTIVES

We evaluated the impact of California's 2006 influenza vaccination requirement for hospital workers (requiring vaccination or signed declinations) on uptake and vaccination-related attitudes, beliefs, and knowledge among hospital HCP.

METHODS

We used a causal difference-in-differences approach to compare changes over the prior 10 years in the self-reported frequency of influenza vaccination for California hospital HCP and those from other states without similar laws using data from a stratified sample (N = 3,529) of HCP drawn from online survey panels. We also examined cross-sectional differences in awareness of vaccination policies, promotion efforts, and attitudes toward influenza vaccination. All analyses used propensity score weighting to balance the observable characteristics of the 2 samples.

RESULTS

We found that compared with their counterparts in other states, California hospital HCP were (1) more likely to report working under a formal written policy for influenza vaccination, (2) no more likely to be vaccinated, and (3) less likely to report working for an employer who provided financial incentives for vaccination or rewarded or recognized employees for being vaccinated.

CONCLUSION

Our results suggest that state-level vaccination requirements such as those enacted by California, may not be sufficient to increase uptake among hospital HCP.

The impact of value-based benefit design on adherence to diabetes medications: a propensity score-weighted difference in difference evaluation

OBJECTIVE

To evaluate the impact of value-based benefit design (VBBD) on adherence to diabetes medications.

METHODS

Health Alliance Medical Plans piloted VBBD for diabetes medications for a subgroup of 5400 enrollees in January 2007 while keeping drug benefits unchanged for the remaining plan enrollees. A difference in difference method (DID) was used to evaluate the effect of VBBD based on pharmacy claim data. Patients with unchanged benefits in the same plan were used as the control group. Adherence was measured by the proportion of days covered. Propensity score weighting was used to balance characteristics of the case group and the control group.

RESULTS

There were 71 patients in the case group and 5037 patients in the control group. The patients in the two groups had comparable characteristics after propensity score weighting. After the implementation of VBBD, the average copayment per 30 days of supply for diabetes medications decreased from $15.3 to $10.1 for the case group and increased from $14.6 to $15.1 for the control group. The probability of being adherent increased from 75.3% to 82.6% for the case group and was roughly unchanged from 79.1% to 78.5% for the control group. Propensity score-weighted DID analysis showed that patients with copayment reduction had greater odds of being adherent: odds ratio=1.56, P=0.03, 95% confidence interval 1.04-2.34.

CONCLUSION

A VBBD program that reduced the copayment for diabetes medications by 36.1% reduced the number of nonadherent patients by 30.0%.

Impact of concurrent macrovascular co-morbidities on healthcare utilization in patients with type 2 diabetes in Europe: a matched study

AIM

To examine and to quantify the impact of concurrent macrovascular co-morbidities (MVC) on healthcare resource utilization among patients with type 2 diabetes mellitus (T2DM) in Europe.

METHODS

This is a matched cohort study based on the Real-Life Effectiveness and Care Patterns of Diabetes Management study, a multicentre, observational study with retrospective medical chart reviews of T2DM patients in Spain, France, UK, Norway, Finland, Germany and Poland. Included patients were aged > or =30 years at time of diagnosis of T2DM who added a sulfonylurea or a PPARgamma agonist to failing metformin monotherapy (index date) and had concurrent MVC (cases). A control cohort with T2DM but without concurrent MVC was identified using 1:1 propensity score matching. Logit models were used to identify the relationship between concurrent MVC and the likelihood of emergency room admission, receiving medical/surgical procedures, and hospitalization during the study period after controlling for baseline demographics, clinical information and baseline treatment. Negative binomial models were used to predict the number of office visits and length of hospital stay per year attributable to the concurrent MVC.

RESULTS

Relative to controls, patients with MVC were significantly more likely to have emergency department admissions [odds ratio (OR) 2.69; 95% CI: 1.56-4.65], receiving medical/surgical procedures (OR 2.57; 95% CI: 1.56-4.21) and hospitalizations (OR 2.58; 95% CI: 1.64-4.07) after controlling for other predictors. Similarly, MVC were associated with 1.49 additional office visits per year (p = 0.036) and 0.32 days of hospital stay per year (p = 0.023).

CONCLUSIONS

Within a seven-country European sample, this study showed that T2DM patients with MVC were more likely to use healthcare resources compared with T2DM patients without MVC.

Healthcare costs of atypical antipsychotic use for patients with bipolar disorder in a Medicaid programme

BACKGROUND

A large body of clinical studies have demonstrated the efficacy of atypical antipsychotic use in the treatment of bipolar disorder. Facing increasing budget pressure, third-party payers, such as state Medicaid programmes in the US, are demanding better understanding of the medical costs beyond atypical antipsychotic drug costs alone in treating bipolar disorder.

OBJECTIVE

To examine healthcare costs associated with the atypical antipsychotic treatments for bipolar disorder from a US third-party payer perspective.

METHODS

This was a retrospective cohort study using an intent-to-treat approach. Using the North Carolina Medicaid claims database (August 2000 to January 2005), 3328 patients with bipolar disorder were identified who were continuously eligible for 3 months pre-initiation and 12 months post-initiation of treatment with an atypical antipsychotic (AP2) or mood stabilizer (MS). Patients were classified into three groups based on the treatment types during the first 30 days after treatment initiation: AP2 monotherapy, AP2 + MS combination therapy, and MS monotherapy. Bipolar-related and total health-related costs were examined for the 12-month period. Propensity score matching was employed to balance baseline characteristics among the three comparison groups. Generalized linear models were further employed to estimate the average treatment effect on the cost outcomes.

RESULTS

Compared with MS monotherapy, AP2 monotherapy and AP2 + MS combination therapy incurred higher medication costs during the 12-month treatment period. Patients receiving AP2 monotherapy had significantly lower bipolar-related medical costs (-$US698; p = 0.002) [year 2004 values] than patients receiving MS monotherapy. However, the inclusion of the medication cost produced no statistically significant difference in bipolar-related total cost (p = 0.14). Similar results were observed for all health-related costs. Patients receiving AP2 + MS therapy incurred significantly higher bipolar-related total costs (+$US1659; p < 0.0001) and all health-related total costs (+$US2115; p < 0.0001) than patients receiving MS monotherapy, which was attributable largely to the higher medication cost.

CONCLUSIONS

From a third-party payer perspective, atypical antipsychotic monotherapy generated higher drug costs but lower medical care costs, resulting in equivalent total healthcare costs over a 1-year period.

Cost analysis in a Medicaid program for patients with bipolar disorder who initiated atypical antipsychotic monotherapy

BACKGROUND

Use of atypical antipsychotics in treatment of patients with bipolar disorder is increasingly common, yet few studies have systematically investigated or compared medical costs associated with use of specific atypical antipsychotics.

OBJECTIVE

To evaluate the direct healthcare costs associated with olanzapine, risperidone, or quetiapine monotherapy among Medicaid patients diagnosed with bipolar disorder (ICD-9: 296.4x-296.8x).

METHODS

North Carolina Medicaid patients with bipolar disorder were followed for 12 months after initiation of atypical antipsychotic monotherapy (index date). They had no bipolar-related medical visit, hospitalization, or use of atypical antipsychotics 90-days prior to the treatment initiation. Costs of index drug, all bipolar-related medical care, and all health-related costs were examined. A two-stage sample selection model was employed to account for potential confounders and sample selection bias. Medication adherence measures using cumulative medication acquisition and cumulative medication gap were calculated as separate outcomes.

RESULTS

Inclusion criteria were met by 838 continuously eligible patients (393 olanzapine, 262 risperidone, 183 quetiapine). Drug-taking adherence was similar across the drug cohorts. After adjusting for potential confounders, patients taking olanzapine incurred $863 (p < 0.001) and $449 higher (p < 0.01) index drug costs than patients taking risperidone and quetiapine, respectively. Bipolar-related medical costs for patients taking olanzapine were higher ($616; p = 0.06) than for patients taking risperidone at 10% significance level, while such costs for patients taking olanzapine and quetiapine were similar. Total health-related costs did not differ across patient cohorts, including or excluding the index drug costs.

LIMITATIONS

The final study sample is a highly selected one based on the study design. This sample may not represent the entire bipolar population. The criteria used to guard against omitting bipolar disorder patients misdiagnosed with major depression need further validation.

CONCLUSIONS

No evidence was identified that there is any difference for total health-related costs in using olanzapine, risperidone, or quetiapine monotherapy to treat bipolar disorder, from a Medicaid payer's perspective. The clinical difference between these atypical antipsychotic drugs for the treatment of bipolar disorder could be of more interest than the economic difference.