Fluoxetine and dothiepin therapy in primary care and health resource utilization: Evidence from the United Kingdom

The use of linear instrumental variables methods in health services research and health economics: a cautionary note

OBJECTIVE

To investigate potential bias in the use of the conventional linear instrumental variables (IV) method for the estimation of causal effects in inherently nonlinear regression settings.

DATA SOURCES

Smoking Supplement to the 1979 National Health Interview Survey, National Longitudinal Alcohol Epidemiologic Survey, and simulated data.

STUDY DESIGN

Potential bias from the use of the linear IV method in nonlinear models is assessed via simulation studies and real world data analyses in two commonly encountered regression setting: (1) models with a nonnegative outcome (e.g., a count) and a continuous endogenous regressor; and (2) models with a binary outcome and a binary endogenous regressor.

PRINCIPAL FINDINGS

The simulation analyses show that substantial bias in the estimation of causal effects can result from applying the conventional IV method in inherently nonlinear regression settings. Moreover, the bias is not attenuated as the sample size increases. This point is further illustrated in the survey data analyses in which IV-based estimates of the relevant causal effects diverge substantially from those obtained with appropriate nonlinear estimation methods.

CONCLUSIONS

We offer this research as a cautionary note to those who would opt for the use of linear specifications in inherently nonlinear settings involving endogeneity.

Two-stage residual inclusion estimation: addressing endogeneity in health econometric modeling

The paper focuses on two estimation methods that have been widely used to address endogeneity in empirical research in health economics and health services research-two-stage predictor substitution (2SPS) and two-stage residual inclusion (2SRI). 2SPS is the rote extension (to nonlinear models) of the popular linear two-stage least squares estimator. The 2SRI estimator is similar except that in the second-stage regression, the endogenous variables are not replaced by first-stage predictors. Instead, first-stage residuals are included as additional regressors. In a generic parametric framework, we show that 2SRI is consistent and 2SPS is not. Results from a simulation study and an illustrative example also recommend against 2SPS and favor 2SRI. Our findings are important given that there are many prominent examples of the application of inconsistent 2SPS in the recent literature. This study can be used as a guide by future researchers in health economics who are confronted with endogeneity in their empirical work.

Economic evaluation of antidepressive agents: a systematic critique of experimental and observational studies

The purpose of this study was to examine whether experimental and observational pharmacoeconomic analyses of antidepressant drugs support the choice of one of the selective serotonin reuptake inhibitors or newer antidepressants as first-line treatment for patients with major depression. We systematically reviewed economic evaluations of two or more antidepressants completed in clinical practice. A systematic electronic search yielded 38 studies meeting the inclusion criteria, of which 23 were administrative database analyses, 12 were observational studies, and 3 were randomized clinical trials. Experimental data indicated that tricyclic antidepressants are equivalent to selective serotonin reuptake inhibitors in terms of total expenditure. While the database analyses are susceptible to bias and confounding variables, they provided an added dimension based on observations from everyday clinical practice. The majority of these studies failed to show any significant difference. Taken together, available pharmacoeconomic studies indicate that tricyclic drugs and selective serotonin reuptake inhibitors have similar cost effectiveness in the health care systems where these comparisons have been made.

Antidepressant selection and economic outcome: a review of methods and studies from clinical practice

BACKGROUND

Economic considerations increasingly play a role in the selection of antidepressant drugs and are often based on analyses from prospective and retrospective studies. However, the non-randomisation found in retrospective studies may result in significant selection bias.

AIMS

To highlight the use of statistical methods in non-randomised studies and the application of those methods to economic analyses.

METHOD

The literature on the observational studies of economic outcomes with alternative antidepressants is reviewed and several statistical methodologies to control for biases that can occur in non-randomised study designs are described.

RESULTS

In comparisons of antidepressant drugs, differences in acquisition costs are consistently found to be at least offset by other components of care when broad measures of health care resource utilisation are considered.

CONCLUSIONS

Economic evaluations of antidepressants should be based on broad measures of health care expenditure and can rely on data generated in real-world settings if appropriate statistical methods are used to control for the potential biases of non-randomisation.

Retrospective analysis of the health-care costs of bupropion sustained release in comparison with other antidepressants

OBJECTIVE

The objective of this study was to evaluate the health care costs associated with the treatment of a new episode of depression with bupropion sustained release (SR) rather than with other antidepressants (selective serotonin reuptake inhibitors [SSRIs], tricyclic antidepressants [TCAs], and serotonin norepinephrine reuptake inhibitors [SNRIs]).

METHODS

This was a retrospective cohort study based on the private-pay, fee-for-service 1997 and 1998 MEDSTAT MarketScan databases. Individuals were included if they were 18 years of age or older, had an initial prescription for an antidepressant under study with an index prescription date between July 1997 and June 1998, and had a claim for a diagnosis of depression diagnosis within 30 days of the index date. All patients' claims from six months before and after receiving their index antidepressant prescription were examined. Total, outpatient, and pharmacy costs were compared among antidepressant groups using an intent-to-treat analysis with exponential regression models and bootstrapped 95% confidence intervals.

RESULTS

A total of 1771 patients were included in the study cohort. The mean age was 41.6 years, and 69.5% of subjects were female. Most patients (75%) continued with the index antidepressant during the 6-month follow-up period. Although the drug acquisition cost was lowest for TCAs, total costs were significantly higher for patients treated with TCAs than for those treated with bupropion SR (p < .05). In comparison with bupropion SR, patients initiating therapy with sertraline had significantly higher mental health payments (p < .05).

CONCLUSIONS

Initiating treatment of depression with bupropion SR was associated with lower total mental health care costs compared with TCAs and with sertraline. This study reaffirms that formulary and medical decision-makers should consider the overall impact of antidepressant treatment, including but not limited to drug acquisition costs, other health care costs, and drug efficacy and safety.

Antidepressant use in clinical practice: efficacy v. effectiveness

BACKGROUND

Although the efficacy of antidepressants has been demonstrated in randomised, controlled clinical trials, it is how an antidepressant is used in clinical practice that determines its clinical effectiveness, or real-world efficacy.

AIMS

To explore the frequency with which antidepressants are used at adequate dose and duration to obtain remission of symptoms and prevent relapse in clinical practice and discuss potential implications for clinical outcomes.

METHOD

Studies of antidepressant prescribing were reviewed and comparisons made between antidepressant classes and individual compounds within those classes.

RESULTS

Naturalistic studies show that patients who begin therapy on tricyclic antidepressants often receive sub-therapeutic doses for inadequate duration; conversely, patients who begin therapy on selective serotonin reuptake inhibitors more often receive an adequate dose of therapy for a longer duration. CONCLUSIONS; How antidepressants are used in clinical practice can determine the clinical outcomes that are achieved. Antidepressants that are more forgiving of sub-optimal prescribing and use patterns by providers and patients, respectively, may help to improve real-world efficacy.

Estimating endogenous treatment effects in retrospective data analysis

Treatment effect estimation is one of the mainstays of the field of outcomes research. It is, for example, a key component in analyzing the cost-effectiveness of a proposed qualitative intervention. Some outcomes researchers are hesitant to use retrospective data for treatment effect estimation because of the potential endogeneity of the treatment variable. This is unfortunate, given the abundance and other advantages of retrospective data. Others who have used retrospective data have ignored the endogeneity problem, or have not recognized its potential for causing bias in their estimates. In this paper, an econometric method that is unbiased in the presence of endogeneity and therefore broadens the potential for use of retrospective data in the estimation of treatment effects is proposed. This two-stage method is also designed to accommodate nonlinearity in the relationship between the treatment variable and the outcome. An easy to apply GAUSS implementation of the estimator is offered.