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PubMedDate not supplied

The instrumental variable method to study self-selection mechanism: a case of influenza vaccination.

OBJECTIVE: To assess whether estimates of the effectiveness of influenza vaccination in reducing rates of hospitalizations and all-cause mortality derived from cross-sectional data could be improved by applying the instrumental variable (IV) method to data representing the community-dwelling elderly population in the United States in order to adjust for self-selection bias. METHODS: Secondary data analysis, using the 1996-97 Medicare Current Beneficiary Survey data. First, using single-equation probit regressions this study analyzed influenza-related hospitalization and death due to all causes predicted by vaccination status, which was measured by claims or survey data. Second, to adjust for potential self-selection of the vaccine receipt, for example, higher vaccination rates among high-risk individuals, bivariate probit (BVP) models and two-stage least squares (2SLS) models were employed. The IV was having either arthritis or gout. RESULTS: In single-equation probit models, vaccination appeared to be ineffective or even to increase the probability of adverse outcomes. Based on BVP and 2SLS models, vaccination was demonstrated to be effective in reducing influenza-related hospitalization by at least 31%. The BVP model results implied significant self-selection in the single-equation probit models. CONCLUSIONS: Adjusting for self-selection, BVP analyses yielded vaccine effectiveness estimates for a nationally representative cross-sectional sample of the community-dwelling elderly population that are consistent with previous estimates based on randomized controlled trials, prospective cohort studies, and meta-analyses. This result suggests that analyses with 2SLS and BVP in particular may be useful for the analysis of observational data regarding prevention in which self-selection is an important potential source of bias.

Aged↗
PubMed1990

Access to medical care for children and adolescents in the United States.

To evaluate access to health care for American children and adolescents, a telephone survey of a national random sample of households was conducted in which 2182 children 17 years or younger were studied. Approximately 10% had no medical insurance; 10% had no regular source of care; and 18% identified emergency rooms, community clinics, or hospital outpatient departments as their usual site of medical care. Children who were uninsured, poor, or nonwhite were less likely to have seen a physician in the past year (P less than .001), and uninsured children were less likely to have up-to-date immunizations. Logistic regression analyses revealed that poor, uninsured, or nonwhite children less frequently had a regular source of care; more frequently used emergency rooms, community clinics, and hospital outpatient departments as their regular providers; and more frequently encountered financial barriers to health care. Low-income or nonwhite children had much less access to care compared with children from more affluent or white families, independent of insurance status or health status.

Adolescent↗
PubMed2001

[Effect of a back education program by the Lower Saxony AOK in response to the development of health related quality of life and occupational disability].

The statutory sickness fund AOK Lower Saxony developed a specific course program for a target group of up to 55-year old employees with common back pain in the early satge of chronification. Comparative evaluation of effects in study participants and controls was achieved by quality of life and performance data, i.e. days of sick leave (DSL). Medium and long-term change inquality of life (6 and 12 months after the course) was assessed by means of the SF-36 dimensions for cases and controls and compared in bivariate and multivariate test. 92 of 197 baseline participants (or 127 participants who completed the programme) and 483 controls were included in the medium term effect analysis. Significant medium and long-term net efffects could only be shown for pain dimensions. Anonymised DSL data for all 5409 insured persons who were initially selected as potiential participants for the regionally restricted course programme in the second quarter of 1997 were available for the period from 01-01-1996 to 30-06-1999. For controlling any selection bias and potential regional differences, the initial DSL trends of the 197 baseline course participants were compared with two control groups, namely other insured from the programme region and control regions. DSL trends in the three groups prior to the course program were identical. Subsequently DSL due to ICD-9 Codes 710-739 were reduced more substantially in course participants than in controls: 25.5 versus 33 or 32 days respectively. A covariance analysis model that also considered socio-economic factors and pre-intervention DSL levels yeilded a 14-day reduction in DSL (p value 0.023). This is a clear effect on DSL trends taht may be utilised for net savings for AOK. This is also the first proof of a backpain programme outside company settings taht permits net savings.

Curriculum↗
PubMed1984

Health care experience among employees prior to and after enrollment in a prepaid health insurance plan (HMO).

Company medical and benefit records of employees who were enrolled in prepaid health insurance plans (HMOs) in Minneapolis, Washington, D.C., and Seattle were reviewed for hospital and surgical utilization prior to as well as after their enrollment. Comparisons were made for the same calendar periods with closely matched employees who were covered by Blue Cross/Blue Shield (BC/BS). The results indicate that after enrollment the HMO subjects at each location had lower rates for hospital and surgical utilization than the BC/BS controls. For the period prior to enrollment, during which time coverage was through BC/BS, the prospective HMO subjects at two locations had lower hospital and surgical utilization than the controls. Possible explanations of this potential self-selection bias are discussed.

Adult↗
PubMed1999

The impact of medical savings accounts on Medicare program costs.

The 1997 Balanced Budget Act provided for a medical savings account (MSA) Medicare demonstration program. This study simulates the impact on Medicare costs of permitting beneficiaries to enroll in MSAs, using a 23,576-person sample of Medicare beneficiaries in 1992. Our simulations differed with respect to assumptions about supplementary insurance coverage, whether the government or the private sector offers MSA coverage, the degree of selection bias, and the size of the induction effects.

Costs and Cost Analysis↗
PubMed1985

Health plan selection in the Federal Employees Health Benefits Program.

A survey of over 8,500 employees of the U.S. Department of Health and Human Services (DHHS) during the May 1982 open season, supplemented by enrollment data for all DHHS employees enrolled in the Federal Employees Health Benefits Program (FEHBP), was used to study insurance plan selection when multiple fee-for-service options as well as HMOs are available. There is evidence of biased selection of health risks in the FEHBP, yet historically the program has exhibited considerable stability. The stability may be attributable partly to control over entry and over changes in benefits and premiums and partly to inertia on the part of enrollees. In spite of large changes in relative premiums and benefits, only 21 percent of all enrollees in the DHHS switched plans during the May 1982 open season. Those employees who did switch plans astutely identified bargains; on average they lowered their annual contribution to premium by almost 40 percent while maintaining the level of benefits. Insurance plans offering relatively generous coverage of a particular service attract a disproportionately high share of enrollees who expect substantial use of that service. The extent of adverse or beneficial selection into HMOs depends on the price and the comprehensiveness of benefits of each available fee-for-service option.

Community Participation↗
PubMed1990

Biased selection under the senior health plan prior use capitation formula.

A widely acknowledged shortcoming of the current AAPCC capitation formula for Medicare HMOs is its inability to adjust capitation levels for differences in health status among enrolled groups. Prior use models have been proposed as one alternative to the current AAPCC risk classes. From 1984 through 1987, Senior Health Plan (SHP) participated in a HCFA-sponsored demonstration project in which capitation payments were determined by a prior use formula incorporating information on inpatient hospital days and Part B deductibles. This paper contains findings about selection bias in SHP enrollment from analyses of preenrollment reimbursements and postenrollment mortality rates of SHP enrollees compared with Medicare FFS beneficiaries and enrollees of other Medicare HMOs in the Minneapolis-St. Paul area.

Capitation Fee↗
PubMed1998

Selection of controls in database case-control studies: glucocorticoids and the risk of glaucoma.

In case-control studies conducted using computerized databases, controls are often selected as a random sample from the base population. This representative choice of controls is intended to guard against selection bias. We show, using data from a database case-control study, that such a definition of controls may also lead to selection bias under two conditions: (1) if the target disease has a prolonged asymptomatic clinical course with its detection depending on a specific physical examination and (2) if exposed patients have a higher likelihood of having the disease detected than unexposed patients. The extent of the bias that could result from the use of randomly selected controls was investigated in the context of a case-control study of the risk of ocular hypertension or glaucoma associated with the use of glucocorticoids, conducted using the Quebec universal health insurance computerized databases. This article also illustrates that a computerized database can be useful to empirically explore opportunities for bias.

Aged↗
PubMed1994

Dentists' response to financial incentives in a mail survey of malpractice liability experience.

This two-part methodologic research was designed to evaluate the effects of a financial incentive on questionnaire response rate and response bias for general dentists surveyed by mail. Subjects were 517 clinicians randomly selected from a two-state population of practitioners insured by a single malpractice liability carrier. Subjects received a check for either $5 or $10 in the original mailing. In Study 1, a single mailing and postcard follow-up resulted in a 57.8 percent (111/192) response rate. In Study 2, employing Dillman's Total Design Method, a 69.6 percent (208/299) response was obtained after a third mailing. Analysis of response rate by incentive level in each study revealed no significant differences. In contrast, early responders (first mailing and follow-up postcard) differed from late responders (second and third mailings) on age (41.4 vs 37.0 years; T = 2.17; P = .032), non-Caucasians (27.7% vs 63.9%; chi 2 = 17.3; df = 4; P < .002), females (13.9% vs 27.8%; chi 2 = 3.9; df = 1; P < .05), foreign-trained (7.0% vs 19.4%; chi 2 = 16.5; df = 2; P < .001), and dissatisfaction with practice (31% vs 51%; chi 2 = 7.8; df = 4; P = .10). Thus, the magnitude of the financial incentive in this experiment had no differential effect on response rate. But differences in responses from late responders (proxies for nonresponders) on demographic characteristics and key study variables suggest the persistence of response bias despite an acceptable response rate. Future dental health survey research should employ tests for response bias on both sets of variables.

Adult↗
PubMed1999

Misclassification and selection bias when identifying Alzheimer's disease solely from Medicare claims records.

BACKGROUND: Medicare claims as the basis for health condition adjustments is becoming a method of choice in capitation reimbursement. A recent study has found that claims-based beneficiary classification for Alzheimer's disease produces lower prevalence estimates and higher average costs than previous healthcare cost studies in this population. These sets of studies differ in data sources, period length, and in their specification of dementia. OBJECTIVES: Participants in the Medicare Alzheimer's Disease Demonstration (MADDE) provide a sample of persons known to have some form of dementia. This group is used to test the adequacy of claims data for identifying eligible cases and any bias in expenditure differences between those flagged or not flagged by a claim in a given period. DESIGN: A prospective cohort design using up to 36 months of claims data. SETTING: The demonstration enrolled 4166 participants in treatment, and 3942 in a control group in eight communities across the US. Cases were combined in this analysis. PARTICIPANTS: Persons with available Medicare Part A & B claims data: those receiving care under fee for service reimbursement were used in the analysis. A total of 5379 MADDE cases received fee for service care during 1991 and 1992, the period of primary interest in the analysis. MEASUREMENT: Client health and functional status interviews and Medicare Part A & B claims. RESULTS: Less than 20% of MADDE participants were classified with Dementia of the Alzheimer type (DAT) from a single year of claims although 68% had a DAT diagnosis from a referring physician. Annualized expenditures were 1.7 times higher among those with DAT from claims compared with those known otherwise to have dementia but who had not been identified with this condition from Medicare claims. CONCLUSION: Underclassification of dementia from claims records can be partially remedied by increasing the period during which claims are compiled, but additional diagnostic sources will likely be needed to increase prevalence counts closer to 100% of true cases. Risk adjustment based on a single year of reported claims expenditures may overpay providers, at least in the short term, because payment incentives will likely increase prevalence reporting.

Aged↗
PubMed1990

Use of telephone interviewing in health care research.

Increasingly, telephone interviewing has become the data collection procedure of choice in large-scale health services research surveys. Previous analyses indicate that excluding nontelephone households does not seriously affect most national parameter estimates, such as yearly estimates of number of ambulatory visits, mainly because the proportion of households without telephones is small. Moreover, if the exclusion of nontelephone households simply underestimates the proportions in the population with certain characteristics, such as age and ethnicity, and the "true" proportions are known, it is possible to appropriately weight the study group in order to mitigate the telephone-exclusion bias. However, regression analyses undertaken on three years of national Health Interview Surveys indicate, at least on some key measures such as having health insurance, that persons living in households with and without telephones represent different populations, and parameter estimates are distorted by excluding nontelephone households. Under these circumstances, it is not possible to adjust parameter estimates to take into account nontelephone households.

Ambulatory Care↗
PubMed2006

Uterine artery embolization as a treatment option for uterine myomas.

Information is still being collected on the long-term clinical responses and appropriate patient selection for UAE. Prospective RCTs have not been performed to compare the clinical results from UAE with more conventional therapies for symptomatic uterine leiomyomata. At least three attempts at conducting such RCTs have been unsuccessful because of poor patient accrual that related to differing patient expectation and desires, clinical bias, insurance coverage, and the tendency that patients who have exhausted other treatment options may be disposed more favorably to less invasive treatments. Other comparative studies have serious limitations. For example, the retrospective study that compared outcomes after abdominal myomectomy with UAE suggested that patients who received UAE were more likely to require further invasive treatment by 3 years than were recipients of myomectomy. Lack of randomization introduced a selection bias because women in the group that underwent UAEwere older and were more likely to have had previous surgeries. A prospective study of "contemporaneous cohorts," which excluded patients who had sub-mucosal and pedunculated subserosal myomas, sought to compare quality of life measures and adverse events in patients who underwent UAE or hysterectomy. The investigators concluded that both treatments resulted in marked improvement in symptoms and quality of life scores, but complications were higher in the group that underwent hysterectomy over 1 year. In this study,however, a greater proportion of patients who underwent hysterectomy had improved pelvic pain scores. Furthermore, hysterectomy eliminates uterine bleeding and the risk for recurrence of myomas. Despite the lack of controlled studies that compared UAE with conventional surgery, and despite limited extended outcome data, UAE has gained rapid acceptance, primarily because the procedure preserves the uterus, is less invasive, and has less short-term morbidity than do most surgical options. The cost of UAE varies by region, but is comparable to the charges for hysterectomy and is less expensive than abdominal myomectomy. The evaluation before UAE may entail additional fees for diagnostic testing, such as MRI, to assess the uterine size and screen for adenomyosis. Other centers have recommended pretreatment ultrasonography, laparoscopy, hysteroscopy, endometrial biopsy, and biopsy of large fibroids to evaluate sarcoma. Generally,after UAE the recovery time and time lost from work are less; however, the potential need for subsequent surgery may be greater when compared with abdominal myomectomy. Any center that offers UAE should adhere to published clinical guidelines,maintain ongoing assessment of quality improvements measures, and observe strict criteria for obtaining procedural privileges. After McLucas advocated that gynecologists learn the skill to perform UAE for managing symptomatic myomas, the Society of Interventional Radiology responded with a precautionary commentary on the level of technical proficiency that is necessary to maintain optimum results from UAE. The complexity of pelvic arterial anatomy, the skill that is required to master modern coaxial microcatheters, and the hazards of significant patient radiation exposure were cited as reasons why sound training and demonstration of expertise be obtained before clinicians are credentialed to perform UAE.A collaboration between the gynecologist and the interventional radiologist is necessary to optimize the safety and efficacy of UAE. The primary candidates for this procedure include women who have symptomatic uterine fibroids who no longer desire fertility, but wish to avoid surgery or are poor surgical risks. The gynecologist is likely to be the primary initial consultant to patients who present with complaints of symptomatic myomas. Therefore, they must be familiar with the indications, exclusions, outcome expectations, and complications of UAE in their particular center. When hysterectomy is the only option, UAE should be considered. Appropriate diagnostic testing should aid in the exclusion of most, but not all, gynecologic cancers and pregnancy. Other contraindications include severe contrast medium allergy, renal insufficiency, and coagulopathy. MRI may be used to screen women before treatment in an attempt to detect those who have adenomyosis; patients should be aware that UAE is less effective in the presence of solitary or coexistent adenomyosis. Because some women may experience ovarian failure after UAE, additional studies to determine basal follicle-stimulating hormone and estradiol before and after the procedure may provide insight into UAE-induced follicle depletion.UAE is a unique new treatment for uterine myomas, and is no longer considered investigational for symptomatic uterine fibroids. There is international recognition that data are needed from RCTs that compare UAE with surgical alternatives. Current efforts to provide prospective objective assessment of treatment outcomes and complications after UAE will help to optimize patient selection and clinical guidelines. FIBROID should provide critical data for the assessment of safety and outcomes measures for women who receive UAE for symptomatic uterine myomas.

Angiography↗
PubMed1998

Is spa therapy cost-effective in rheumatic disorders?

OBJECTIVE: To evaluate the cost-effectiveness of spa therapy for rheumatic diseases and sequelae of bone and joint injuries. PATIENTS AND METHODS: A prospective randomized, case-control design was used with health care cost reimbursements during the year before and after spa therapy as the measure of efficacy. Spa therapy is reimbursed by the national health insurance system in France, subject to prior agreement. The 220 patients who filed applications for spa therapy with the national health insurance payment center for northern France during the first half of 1994 were included in the study. Seventy-two patients met national health insurance system criteria for spa therapy (Group 1), the remaining 148 patients were assigned at random to spa therapy (Group 2, n = 74) or no spa therapy (Group 3, n = 74). This method allowed us to avoid selection bias during recruitment of our control group. RESULTS: Perceived morbidity was evaluated based on health care utilization, expressed as numbers of health care investigations or procedures and as days of medication use in mean recommended dosages. Health care cost reimbursements by the national health insurance system failed to decrease during the year after spa therapy, and increased in those patients who had already received spa therapy on one or more occasions. Only in the first-ever spa patients were decreases in health care utilization in the area of rheumatology seen during the year after spa therapy; the largest decreases were for use of nonsteroidal antiinflammatory drugs (from 49 to 26 days) and muscle relaxants. No differences in health care utilization were found in patients who had received spa therapy on at least one other occasion. Also, when criteria for spa therapy were not met, no differences in health care utilization were found between patients who did and did not receive spa therapy. CONCLUSION: These data suggest that current national health insurance policies regarding the reimbursement of spa therapy need to be reevaluated.

Age Factors↗
PubMed1991

Case-control evaluation of breast cancer screening efficacy.

The feasibility and validity of using case-control methods to evaluate the efficacy of breast cancer screening were investigated using data from the Health Insurance Plan of Greater New York Breast Cancer Screening Trial. Women who died of breast cancer were compared with individually matched controls of the same age who had equal or greater survival times. To minimize the effects of self-selection bias, most analyses focused on the 95 cases and 380 matched controls who had been screened at least once and for whom covariate data were available. A statistically significant effect for being screened more than once versus being screened once, uncorrected for healthy-screenee bias, was found (odds ratio = 0.13, p less than 0.001). After correction for healthy-screenee bias, the effect was not statistically significant (odds ratio = 0.54, p = 0.15). Possible explanations for this statistical nonsignificance are: 1) correction for healthy-screenee bias entails loss of power and 2) the correction procedure used may, under some circumstances, result in bias toward the null hypothesis. Further research into means of eliminating healthy-screenee bias is needed to improve the applicability of case-control methods to the evaluation of screening efficacy.

Adult↗
PubMed1996

Modifying managed competition to address cost and quality.

California's health care marketplace is undergoing rapid transformation--from one characterized by aggressive but unregulated competition to one that approximates managed competition. The Pacific Business Group on Health purchases health insurance for large employers; the California Public Employees Retirement System acts as a purchasing pool for both state workers and smaller public employers; and The Health Insurance Plan of California is a pool for small employers. Each focuses on price-conscious competition among health maintenance organizations. These large purchasing cooperatives also are addressing biased selection among the health plans they offer. Initially focused on simple demographic adjustments, risk adjustment now also entails adjustment for high-risk cases, such as acquired immunodeficiency syndrome (AIDS) and liver transplants. These purchasers also devote more detailed attention to the quality and process of care.

Acquired Immunodeficiency Syndrome↗