SEARCH · Search PubMed

Results for “instrumental variable”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10Linked to original sources

PubMed1999

Video-assisted thoracoscopic surgery to the upper thoracic spine.

BACKGROUND: The standard open technique for exposure of the upper thoracic spine, T1-T4, usually requires a difficult thoracotomy. From November 1, 1995 to June 30, 1997, eight patients underwent video-assisted thoracoscopic spinal surgery in our institute to treat their upper thoracic spinal lesions endoscopically. METHODS: A new approach, the so-called "extended manipulating channel method," was used in this series that allows the combined use of video-assisted thoracoscopy and conventional spinal instruments to enter the chest cavity freely for the procedures. Patients' ages ranged from 44 to 89 years (average, 60 years). Definitive diagnoses included two pyogenic spondylitis and six spinal metastases. Five patients presented initially with myelopathy. RESULTS: There were no deaths or neurologic injuries associated with this technique. The mean surgical time was 3.1 h. The mean duration of chest tube retention was 3.3 days. The mean total blood loss was 1,038 ml, and two patients had a blood loss of more than 2,000 ml owing to bleeding from epidural veins or raw osseous surfaces. Complications included one superficial wound infection and one subcutaneous emphysema that resolved spontaneously. In this series, there was no need of conversion to open thoracotomy for the patients. CONCLUSIONS: The thoracoscopy-assisted spinal technique using the extended manipulating channels, usually 2.5-3.5 cm, allows variable instrument angulations for manipulation. The mean surgical time (3.1 h) was considered no longer than for an open technique for the equivalent anterior procedure. Such an approach can achieve less procedure-related trauma and has proved to be a good alternative to other treatment modalities.

Adult↗

PubMed1998

The economic benefits of supported employment for persons with mental illness.

BACKGROUND: Policies and programs that emphasize employment for persons with mental illness are often promoted with the goals of improving economic self-sufficiency and reducing dependence on public welfare programs. At present, there is little empirical evidence about the actual effect of vocational interventions on economic self-sufficiency or on use of public benefits by persons with mental illness. STUDY AIMS: This study provides a preliminary look at how participating in supported employment, a form of vocational rehabilitation emphasizing ongoing support in competitive jobs, affects the amount that participants earn from work and the total amount of income they receive from all sources. Further, we examine the extent to which receiving public benefits affects the amount earned from private employment, taking into consideration other factors that might be associated with benefit status. METHODS: Data are from a randomized trial of supported employment interventions. This analysis followed 137 of those study participants with severe mental illness for 18 months after they enrolled in either of two supported employment programs. Income from various sources was estimated based on interviews with study participants upon study entry and at six-month intervals thereafter. Changes in income from work, government and other sources were analyzed using paired Wilcoxon matched-pairs signed-ranks tests and t-tests. Using ordinary least-squares regression, we analyzed the effect of benefit status on changes in earnings, taking into account diagnosis, work history, education, program type, site of program, psychiatric symptoms, global functioning and previous earnings. RESULTS: Estimated total income increased by an average of $134 (US) per month after enrolling in supported employment. More than three-quarters of this increase was from government sources, such as Social Security and educational grants. The increase in government income was largely due to participants applying for and getting cash benefits for the first time. Social Security payments for those receiving benefits before enrollment did not change significantly. A small group of persons (n = 22) who did not receive Social Security benefits before or after enrolment earned significantly more from competitive employment after enrolling than did those who received benefits. This finding persisted after taking into acount differences in work history, clinical and functional variables and education. LIMITATIONS: Because of the relatively small sample size and the lack of continuous measures of income these results should be considered preliminary. CONCLUSIONS: Supported employment, one of the more effective forms of vocational rehabilitation for persons with mental illness, did not reduce dependence on government support. Receiving government benefits was associated with lower earnings from work. IMPLICATIONS FOR HEALTH CARE PROVISION AND USE: These findings suggest that most persons in treatment for severe mental illness need continued public financial support even after enrolling in vocational rehabilitation programs. IMPLICATIONS FOR HEALTH POLICY FORMULATION: Undoubtedly increased labor force participation can benefit persons with mental illness in a number of ways. However, policy makers should be careful about justifying increased access to vocational programs on the basis of reduced spending for income support. Further, targeting such programs only to persons receiving income support may overlook the clients who can benefit most: those who are not currently receiving benefits. IMPLICATIONS FOR FURTHER RESEARCH: Policy makers need a better understanding of how vocational interventions and income support programs affect the income and well-being of persons with mental illness. Studies similar to this one should be repeated with larger, more diverse samples that will allow use of instrumental variables statistical techniques.

Journal Article↗

PubMed2001

Labor Supply of Poor Residents in Metropolitan Miami, Florida: The Role of Depression and the Co-Morbid Effects of Substance Use.

BACKGROUND: Depression represents one of the most common behavioral health problems among the workforce in the United States, with about 1 in every 20 employees experiencing this condition. A recent study estimated that in 1990 the economic costs of depressive disorders in the American workplace amounted to as much as $43 billion, with absenteeism alone accounting for $12 billion. Recently, economists have been focusing attention on the relationship between mental health and labor supply, but a lack of quality data sets containing detailed information on mental health and labor market variables represents a significant barrier to rigorous research. AIMS OF THE STUDY: The primary aims of the present study were to (i) examine the relationship between depression and employment, (ii) conditional on being employed, estimate the effect of depression on annual weeks worked, and (iii) examine the stability of the model estimates to the co-morbid effects of substance use (illicit drugs and alcohol), which has been consistently found to be a correlate of depression. DATA: The study used a unique set of survey data collected between 1996 and 1997 in crime-ridden and low-income neighborhoods of Miami-Dade County, Florida. A targeted sampling strategy was used to recruit chronic drug users (including injection drug users) and non-drug users to examine local health care delivery system characteristics in relation to the population of substance users. The final analysis sample for the present study included 1,274 adults, aged 18 to 65. Depression status was measured from the 20-item Zung Self-Rating Depression Scale (SDS) that classified 384 individuals as depressed and 890 as non-depressed. According to the definition developed by the U.S. Office of National Drug Control Policy for chronic drug use (CDU), about 46 percent of the depressed individuals were found to be CDUs compared to 30 percent of the non-depressed sample. The survey instrument collected information on alcohol use and problem drinking as defined by the 10-item Michigan Alcoholism Screening Test (MAST-10). Based on criteria defined in the MAST-10, 26 percent of the depressed individuals were problematic alcohol users (PAUs) compared to about 16 percent of the non-depressed sample.METHODS: The labor supply measures included employment in the past 30 days and number of weeks worked in the past 12 months. The analysis estimated a univariate probit model of employment as well as a bivariate probit model of depression and employment, which accounted for the possible correlation between the unobserved determinants of depression and employment. The annual weeks worked specification was estimated by a standard Tobit model as well as an instrumental variable (IV) Tobit model, which, in addition to the censoring of the observations, accounted for the possible endogeneity of depression. The stability of the estimated effects of depression to comorbid illicit drug and alcohol use was assessed, by controlling for CDU and PAU in these models. RESULTS: Results from both the univariate probit and the bivariate probit models indicate that depression significantly decreased the probability of being employed. Specifically, depression reduced the probability of employment by an average of 19 percentage points in both models, from a sample average of 43 percent for the non- depressed to 24 percent for the depressed. Estimates from the Tobit models revealed that depression also significantly reduced the number of weeks worked. Conditional on being employed, depressed individuals worked an average of 7 fewer annual weeks than the non-depressed sample in the univariate Tobit model and 8 fewer weeks in the IV Tobit. The findings also showed that the effects of depression on employment and annual weeks worked may be over-estimated if the analysis does not account for the comorbid influence of substance use. IMPLICATIONS FOR HEALTH CARE PROVISION AND USE: The results suggest that prevention and/or treatment of mental health problems such as depression may yield economic benefits by promoting employment and enhancing labor supply. While expansion of public mental health services may not lead to overall increases in employment, it may be justified on social grounds given the high unemployment rate in low-income and crime-ridden neighborhoods. Further insights can be gained by estimating these models with national and international data if one applies appropriate econometric tools to account for complex sample designs.

Journal Article↗

PubMed2006

Social interactions in adolescent television viewing.

OBJECTIVE: To examine whether social interactions influence the television viewing choices of adolescents in grades 7 through 12. DESIGN: Data from a nationally representative cross-sectional survey were used to examine the association between individual-level and school-level television choices. An instrumental variables approach was used to solve the simultaneity problem found in models that examine the association between individual and aggregate choices. SETTING: In-home interviews in the United States collected in 1996. PARTICIPANTS: A sample of 4532 students in grades 7 through 12 in 132 US public and private schools who participated in the National Longitudinal Study of Adolescent Health (Add Health). MAIN EXPOSURE: The reported television viewing choices of an individual's schoolmates. MAIN OUTCOME MEASURE: The number of hours of television individuals reported viewing in a week. RESULTS: The number of hours of television that adolescents report viewing per week was associated with their peers' reported hours of television viewing. Adjusted for other covariates, a 1-hour increase in average school-level television viewing was associated with an increase in almost half an hour of television viewing at the individual level. CONCLUSIONS: Evidence suggests that social interactions within schools influence the hours of television that adolescents report viewing. This finding is important for both future attempts at modeling the determinants of adolescent television viewing and suggestions for future policy interventions. The presence of social interactions implies that interventions that affect the social norms of television viewing within schools could also change individual television viewing. In reducing the number of hours of television watched, these interventions could also positively affect adolescent obesity, emotional problems, and academic achievement.

Adolescent↗

PubMed1996

Flow cytometric HLA-B27 typing using CD3 gating and molecules of equivalent soluble fluorochrome (MESF) quantitation.

The determination of HLA-B27 (B27) status is important in the diagnosis of ankylosing spondylitis, Reiter's disease, and other arthropathies. Flow cytometric (FCM) typing of B27 is a relatively new method which allows for rapid turnaround time and low cost. However, different leukocyte populations may manifest significant variation in staining intensity with B27 antibodies. Therefore, gating utilizing only light scatter properties of cells may lead to high readings in some B27-negative samples. Fluorescence gating on CD3+ cells were postulated as a means to eliminate these anomalies. Furthermore, quantitative FCM measurements, as afforded through use of molecules of equivalent soluble fluorochrome (MESF) units, can minimize day-to-day and instrument-to-instrument variabilities in fluorescence measurements. We compared CD3 gating to light scatter gating and MESF analysis on 123 specimens in a 4-month period and found: 1) CD3 gating gave the lowest nonspecific B27 antibody binding among B27-negative subjects; 2) there was no significant difference in MESF values between CD3 gating and light scatter gating of B27-positive samples; 3) there was a wide range of B27 antibody binding fluorescence intensities among B27-positive subjects; 4) identification of patients with low B27 expression may require the use of CD3 gating in order to avoid costly confirmation testing; 5) fluorescent standard beads are stable for routine use in a clinical flow cytometry laboratory.

Antibodies, Monoclonal↗

PubMed1998

Volume responses to Medicare payment reductions with multiple payers: a test of the McGuire-Pauly model.

The effects of changing financial incentives on physician's practice behaviour have long been of interest to researchers and policy makers. We test a model of physician volume response within the context of multiple payers developed by Thomas McGuire and Mark Pauly. A panel data set covering discharges from about 200 hospitals in the US over 45 months is used to carry out the empirical investigation. A fixed-effect model with generalized least squares and instrumental variable specifications is used to compute empirical evidence of volume responses from eight specialties experiencing varying degrees of Medicare payment reductions following the implementation of Omnibus Budget Reconciliation Acts of 1989 and 1990. The empirical findings are compared with McGuire and Pauly's simulated predictions. We note that in examining physician responses to Medicare payment reductions in the context of a multi-payer environment, it becomes evident that only fixing one payer's reimbursement policy is at best a partial solution to cost containment. We echo observations made by other analysts that physician responses to payment changes can be quite complex. Physicians do not all respond to payment reduction in the same way.

Budgets↗

PubMed1998

More physicians: improved availability or induced demand?

A number of empirical studies have shown that there is a negative association between population:physician ratio and utilization of medical services. However, it is not clear whether this relationship reflects supplier-inducement, the effect of lower prices on patient demand, a supply response to variation in health status, or improved availability. In Norway, patient fees and state reimbursement fees are set centrally. Therefore, the correlation between utilization and population:physician ratio either reflects supplier-inducement, a supply response or an availability effect. We applied a theoretical model which distinguished between an inducement and an availability effect. The model was implemented on a cross-sectional data set which contained information about patient visits and laboratory tests for all fee-for-service primary care physicians in Norway. Since population:physician ratio is potentially endogenous, an instrumental variable approach is used. We found no evidence for inducement either for number of visits or for provision of laboratory services.

Clinical Laboratory Techniques↗

PubMed1999

Women's participation in rural credit programmes in Bangladesh and their demand for formal health care: is there a positive impact?

Within the overall aim of poverty alleviation, development efforts have included credit and self-employment programmes. In Bangladesh, the major beneficiaries of such group-based credit programmes are rural women who use the loans to initiate small informal income-generating activities. This paper explores the benefits of women's participation in credit programmes on their own health seeking. Using data from a sample of 1798 households from rural Bangladesh, conducted in 1991-1992 through repeated random sampling of 87 districts covered by Grameen Bank, Bangladesh Rural Advancement Committee (BRAC) and Bangladesh Rural Development Board (BRDB), this paper addresses the question: does women's participation in credit programmes significantly affect their use of formal health care? A non-unitary household preference model is suggested to test the hypothesis that women's empowerment through participation in these programmes results in greater control of resources for their own demand for formal health care. The analysis controls for endogeneity due to self-selection and other unobserved village level factors through the use of a weighted two stage instrumental variable approach with village level fixed effects. The findings indicate a positive impact of women's participation in credit programmes on their demand for formal health care. The policy simulations on the results of this study highlight the importance of credit programmes as a health intervention in addition to being a mechanism for women's economic empowerment.

Adolescent↗

PubMed1999

On measuring the hospital cost/quality trade-off.

This paper explores the relationship between cost and quality of hospital care. A total operating cost function is estimated for 137 US Department of Veterans Affairs hospitals for 1988-1993 using three rate-based measures of quality as regressors. The high likelihood of the existence of measurement error in quality in the cross section leads to the application of novel instrumental variable techniques. Results suggest that mortality and readmission indices are adjusted inadequately for illness severity. The measure on the failure to follow up inpatient discharges with outpatient care, however, appears to increase cost. The results of this paper underscore a number of practical difficulties and challenges facing government or other systems in evaluating the relative performance of their hospitals.

Cost Control↗

PubMed2006

Gout and the risk of acute myocardial infarction.

OBJECTIVE: To determine if hyperuricemia and gouty arthritis are independent risk factors for acute myocardial infarction (MI) and, if so, whether they are independent of renal function, diuretic use, metabolic syndrome, and other established risk factors. METHODS: We performed multivariable logistic and instrumental variable probit regressions on data from the Multiple Risk Factor Intervention Trial (MRFIT). RESULTS: Overall, there were 12,866 men in the MRFIT who were followed up for a mean of 6.5 years. There were 118 events of acute MI in the group with gout (10.5%) and 990 events in the group without gout (8.43%; P = 0.018). Hyperuricemia was an independent risk factor for acute MI in the multivariable regression models, with an odds ratio (OR) of 1.11 (95% confidence interval [95% CI] 1.08-1.15, P < 0.001). In multivariable regressions in which the above risk factors were used as covariates, gout was found to be associated with a higher risk of acute MI (OR 1.26 [95% CI 1.14-1.40], P < 0.001). Subgroup analyses showed that a relationship between gout and the risk of acute MI was present among nonusers of alcohol, diuretics, or aspirin and among those who did not have metabolic syndrome, diabetes mellitus, or obesity. In separate analyses, a relationship between gout and the risk of acute MI was evident among those with and without those hyperuricemia. CONCLUSION: The independent risk relationship between hyperuricemia and acute MI is confirmed. Gouty arthritis is associated with an excess risk of acute MI, and this is not explained by its well-known links with renal function, metabolic syndrome, diuretic use, and traditional cardiovascular risk factors.

Arthritis, Gouty↗

PubMed2006

Illicit drug use and educational attainment.

This paper uses data from the National Education Longitudinal Study to estimate the association between illicit drug use during high school and the number of years of schooling completed. The analysis accounts for the possibility that drug use is endogenous using two methods: (1) by controlling for individual-level characteristics measured before high school entrance; and (2) by using an instrumental variables method, with state drug policies and 8th grade school characteristics as identifying variables. Findings suggest that marijuana use and cocaine use in high school are associated with reductions in the number of years of schooling completed.

Adolescent↗

PubMed2006

Causal effects of alcoholism on earnings: estimates from the NLSY.

Propensity score matching is used to investigate the causal relationship between alcoholism and earnings in a young cohort of males and females drawn from the 1989 and 1994 National Longitudinal Survey of Youth (NLSY) in order to investigate productivity losses attributed to alcoholism and to quantify these effects. Results suggest that there are productivity losses attributable to alcoholism; that they become more pronounced over the life cycle; and that they differ between men and women. Ways in which estimates from propensity score matching may or may not improve on instrumental variables estimates are discussed.

Adult↗

PubMed2007

Government health expenditures and health outcomes.

This paper provides econometric evidence linking a country's per capita government health expenditures and per capita income to two health outcomes: under-five mortality and maternal mortality. Using instrumental variables techniques (GMM-H2SL), we estimate the elasticity of these outcomes with respect to government health expenditures and income while treating both variables as endogenous. Consequently, our elasticity estimates are larger in magnitude than those reported in literature, which may be biased up. The elasticity of under-five mortality with respect to government expenditures ranges from -0.25 to -0.42 with a mean value of -0.33. For maternal mortality the elasticity ranges from -0.42 to -0.52 with a mean value of -0.50. For developing countries, our results imply that while economic growth is certainly an important contributor to health outcomes, government spending on health is just as important a factor.

Child Mortality↗

PubMed2002

Do competition and managed care improve quality?

In recent years, the US health care industry has experienced a rapid growth of managed care, formation of networks, and an integration of hospitals. This paper provides new insights about the quality consequences of this dynamic in US hospital markets. I empirically investigate the impact of managed care and hospital competition on quality using in-hospital complications as quality measures. I use random and fixed effects, and instrumental variable fixed effect models using hospital panel data from up to 16 states in the 1992-1997 period. The paper has two important findings: First, higher managed care penetration increases the quality, when inappropriate utilization, wound infections and adverse/iatrogenic complications are used as quality indicators. For other complication categories, coefficient estimates are statistically insignificant. These findings do not support the straightforward view that increases in managed care penetration are associated with decreases in quality. Second, both higher hospital market share and market concentration are associated with lower quality of care. Hospital mergers have undesirable quality consequences. Appropriate antitrust policies towards mergers should consider not only price and cost but also quality impacts.

Antitrust Laws↗

PubMed2004

A comparison of the grade of membership measure with alternative health indicators in explaining costs for older people.

An important focus in empirical econometric studies of health care concerns estimation of the relationship with health. This paper describes a non-parametric technique, the grade of membership (GoM) procedure, which is used to construct summary indicators of health. Health status is also assessed using three alternative measures commonly employed in the literature: an index of problems of activities of daily living (ADL), an index of health conditions and overall self-rated health. Using data from a sample of frail older people, the relationship between costs and different measures of health are estimated using ordinary least squares (OLS) and instrumental variables (IV) methods. The results show that health influences costs more strongly than other variables, an effect which persists after controlling for potential endogeneity. It is shown that health can be usefully classified using GoM techniques. An alternative measure, based on an index of ADL, also performs well. Measures based on overall self-assessed health and the number of health conditions present were less satisfactory. Although health indicators derived from GoM techniques may be more theoretically attractive, in terms of capturing more fully the multidimensional nature of health, simpler alternatives such as those based on ADL indices may offer practical computational advantages.

Activities of Daily Living↗

PubMed2005

The impact of diabetes on employment: genetic IVs in a bivariate probit.

Diabetes has been shown to have a detrimental impact on employment and labor market productivity, which results in lost work days and higher mortality/disability. This study utilizes data from the Border Epidemiologic Study on Aging to analyze the endogeneity of diabetes in an employment model. We use family history of diabetes as genetic instrumental variables. We show that assuming that diabetes is an exogenous variable results in an overestimate (underestimate) of the negative impact of diabetes on female (male) employment. Our results are particularly relevant in the case of populations where genetic predisposition has an important role in the etiology of diabetes.

Absenteeism↗

PubMed2005

Correcting for bias when estimating the cost of hospital-acquired infection: an analysis of lower respiratory tract infections in non-surgical patients.

Hospital acquired infections (HAI) are costly but many are avoidable. Evaluating prevention programmes requires data on their costs and benefits. Estimating the actual costs of HAI (a measure of the cost savings due to prevention) is difficult as HAI changes cost by extending patient length of stay, yet, length of stay is a major risk factor for HAI. This endogeneity bias can confound attempts to measure accurately the cost of HAI. We propose a two-stage instrumental variables estimation strategy that explicitly controls for the endogeneity between risk of HAI and length of stay. We find that a 10% reduction in ex ante risk of HAI results in an expected savings of pound 693 ($ US 984).

Bias↗

PubMed2025

Association Analysis of the Circulating Proteome With Sarcopenia-Related Traits Reveals Potential Drug Targets for Sarcopenia.

BACKGROUND: Sarcopenia severely affects the physical health of the elderly. Currently, there is no specific drug available for sarcopenia. This study aims to identify pathogenic proteins and druggable targets for sarcopenia through Mendelian randomization (MR)-based analytical framework. METHODS: A sequential stepwise screening method that includes two-sample MR, Steiger filtering test and colocalization (MRSC) was applied to identify causal proteins associated with sarcopenia-related traits. In the MR analyses, 4372 circulating proteins with valid instrumental variables (IVs) from eight proteomic genome-wide association studies were utilized as exposures, and nine sarcopenia-related traits were utilized as outcomes. IVs were classified into cis-protein quantitative trait loci (pQTLs) and trans-pQTLs based on their positions. We conducted cis-only MRSC analyses and cis + trans MRSC analyses using cis-pQTLs and cis + trans pQTLs as IVs, respectively. Post-MRSC analyses were conducted on the prioritized findings of MRSC, including annotation of protein-altering variants (PAVs), assessment of overlap between pQTLs and expression quantitative trait loci (eQTLs), protein-protein interaction (PPI) analysis, pathway enrichment analysis and annotation of drug targets. Utilizing data from the UK Biobank, we performed an observational study to explore the associations between baseline circulating protein levels and the longitudinal changes in nine sarcopenia-related traits. RESULTS: A total of 181 causal associations for 65 proteins were prioritized by the cis-only MRSC analyses and 227 associations for 91 proteins were prioritized by the cis + trans MRSC analyses. Among the prioritized proteins, the majority of them employed non-PAVs as IVs and most of their cis-pQTLs overlapped with corresponding eQTLs and exhibited consistent directionality, with only one trans-pQTL overlapping with an eQTL. The PPI network of cis-only MRSC-prioritized proteins (p = 4.04 × 10-4) and cis + trans MRSC-prioritized proteins (p = 8.76 × 10-5) showed significantly more interactions than expected. Reactome, KEGG and GO pathway enrichment analyses for cis-only MRSC-prioritized proteins identified 52, 12 and 79 enriched pathways, respectively (adjusted p < 0.05). For proteins identified by cis + trans MRSC analyses, only 15 pathways were enriched through the GO pathway enrichment analyses. In the observational study, 197 circulating proteins were identified to be associated with one or more sarcopenia-related traits (p < 0.05/2923). Among them, the significant associations of CTSB (negative association) and ASGR1 (positive association) with sarcopenia-related traits were observed to have consistent directional associations in both MR-based studies and observational studies. Drug target annotations suggested that 52 MRSC-prioritized proteins and 145 biomarkers are drug targets or druggable. CONCLUSIONS: This study identified 89 potential pathogenic proteins and 197 candidate biomarkers for sarcopenia, providing valuable clues for the development of therapeutic drugs for sarcopenia.

Humans↗